Heres my guide on how to create civ specific heroic and national epics to replace the existing ones.
To do this I first created a new building class in C:\Program Files\Firaxis Games\Sid Meier's Civilization 4\Mods\YOURMODNAME\Assets\XML\Buildings\CIV4Buildi ngClassInfos.xml

The entry is as follows:
<BuildingClassInfo>
<Type>BUILDINGCLASS_TEXAS</Type>
<Description>Texas Culture</Description>
<iMaxGlobalInstances>1</iMaxGlobalInstances>
<iMaxTeamInstances>-1</iMaxTeamInstances>
<iMaxPlayerInstances>-1</iMaxPlayerInstances>
<iExtraPlayerInstances>1</iExtraPlayerInstances>
<bNoLimit>0</bNoLimit>
<DefaultBuilding>BUILDING_TEXAS</DefaultBuilding>
<VictoryThresholds/>
</BuildingClassInfo>


This creates a building class named for the civ you want to modify, in this case Texas. Next I greate the actual building entry in C:\Program Files\Firaxis Games\Sid Meier's Civilization 4\Mods\YOURMODNAME\Assets\XML\Buildings\CIV4Buildi ngInfos.xml

The entry is as Follows:
<BuildingInfo>
<BuildingClass>BUILDINGCLASS_TEXAS</BuildingClass>
<Type>BUILDING_TEXAS</Type>
<SpecialBuildingType>NONE</SpecialBuildingType>
<Description>Texas Culture</Description>
<Civilopedia>TXT_KEY_BUILDING_TEXAS_PEDIA</Civilopedia>
<Strategy>NONE</Strategy>
<Advisor>ADVISOR_MILITARY</Advisor>
<ArtDefineTag>ART_DEF_BUILDING_TEXAS</ArtDefineTag>
<MovieDefineTag>NONE</MovieDefineTag>
<HolyCity>NONE</HolyCity>
<ReligionType>NONE</ReligionType>
<StateReligion>NONE</StateReligion>
<PrereqReligion>NONE</PrereqReligion>
<GlobalReligionCommerce>NONE</GlobalReligionCommerce>
<VictoryPrereq>NONE</VictoryPrereq>
<FreeStartEra>NONE</FreeStartEra>
<MaxStartEra>NONE</MaxStartEra>
<ObsoleteTech>NONE</ObsoleteTech>
<PrereqTech>NONE</PrereqTech>
<TechTypes/>
<Bonus>NONE</Bonus>
<PrereqBonuses/>
<ProductionTraits/>
<PowerBonus>NONE</PowerBonus>
<FreeBonus>NONE</FreeBonus>
<iNumFreeBonuses>0</iNumFreeBonuses>
<FreeBuilding>NONE</FreeBuilding>
<FreePromotion>NONE</FreePromotion>
<CivicOption>NONE</CivicOption>
<GreatPeopleUnitClass>NONE</GreatPeopleUnitClass>
<iGreatPeopleRateChange>0</iGreatPeopleRateChange>
<bTeamShare>0</bTeamShare>
<bWater>0</bWater>
<bRiver>0</bRiver>
<bPower>0</bPower>
<bDirtyPower>0</bDirtyPower>
<bAreaCleanPower>0</bAreaCleanPower>
<bDiploVote>0</bDiploVote>
<bForceTeamVoteEligible>0</bForceTeamVoteEligible>
<bCapital>0</bCapital>
<bGovernmentCenter>0</bGovernmentCenter>
<bGoldenAge>0</bGoldenAge>
<bMapCentering>0</bMapCentering>
<bNoUnhappiness>0</bNoUnhappiness>
<bNoUnhealthyPopulation>0</bNoUnhealthyPopulation>
<bBuildingOnlyHealthy>0</bBuildingOnlyHealthy>
<bNeverCapture>0</bNeverCapture>
<bNukeImmune>1</bNukeImmune>
<bPrereqReligion>0</bPrereqReligion>
<bCenterInCity>0</bCenterInCity>
<iAIWeight>0</iAIWeight>
<iCost>160</iCost>
<iHurryCostModifier>50</iHurryCostModifier>
<iMinAreaSize>-1</iMinAreaSize>
<iConquestProb>0</iConquestProb>
<iCitiesPrereq>4</iCitiesPrereq>
<iTeamsPrereq>0</iTeamsPrereq>
<iLevelPrereq>0</iLevelPrereq>
<iMinLatitude>0</iMinLatitude>
<iMaxLatitude>90</iMaxLatitude>
<iGreatPeopleRateModifier>0</iGreatPeopleRateModifier>
<iGlobalGreatPeopleRateModifier>0</iGlobalGreatPeopleRateModifier>
<iAnarchyModifier>0</iAnarchyModifier>
<iGlobalHurryModifier>0</iGlobalHurryModifier>
<iExperience>0</iExperience>
<iGlobalExperience>0</iGlobalExperience>
<iFoodKept>0</iFoodKept>
<iAirlift>0</iAirlift>
<iAirModifier>0</iAirModifier>
<iNukeModifier>0</iNukeModifier>
<iNukeExplosionRand>0</iNukeExplosionRand>
<iFreeSpecialist>0</iFreeSpecialist>
<iAreaFreeSpecialist>0</iAreaFreeSpecialist>
<iGlobalFreeSpecialist>0</iGlobalFreeSpecialist>
<iMaintenanceModifier>0</iMaintenanceModifier>
<iWarWearinessModifier>0</iWarWearinessModifier>
<iGlobalWarWearinessModifier>0</iGlobalWarWearinessModifier>
<iHealRateChange>0</iHealRateChange>
<iHealth>0</iHealth>
<iAreaHealth>0</iAreaHealth>
<iGlobalHealth>0</iGlobalHealth>
<iHappiness>0</iHappiness>
<iAreaHappiness>0</iAreaHappiness>
<iGlobalHappiness>0</iGlobalHappiness>
<iStateReligionHappiness>0</iStateReligionHappiness>
<iWorkerSpeedModifier>0</iWorkerSpeedModifier>
<iMilitaryProductionModifier>0</iMilitaryProductionModifier>
<iSpaceProductionModifier>0</iSpaceProductionModifier>
<iGlobalSpaceProductionModifier>0</iGlobalSpaceProductionModifier>
<iTradeRoutes>0</iTradeRoutes>
<iCoastalTradeRoutes>0</iCoastalTradeRoutes>
<iGlobalTradeRoutes>0</iGlobalTradeRoutes>
<iTradeRouteModifier>0</iTradeRouteModifier>
<iGlobalPopulationChange>0</iGlobalPopulationChange>
<iFreeTechs>0</iFreeTechs>
<iDefense>0</iDefense>
<iAllCityDefense>0</iAllCityDefense>
<iAsset>0</iAsset>
<iPower>0</iPower>
<fVisibilityPriority>10000.0</fVisibilityPriority>
<SeaPlotYieldChanges/>
<GlobalSeaPlotYieldChanges/>
<YieldChanges>
<iYield>0</iYield>
<iYield>0</iYield>
<iYield>0</iYield>
</YieldChanges>
<CommerceChanges/>
<ObsoleteSafeCommerceChanges>
<iCommerce>0</iCommerce>
<iCommerce>0</iCommerce>
<iCommerce>0</iCommerce>
</ObsoleteSafeCommerceChanges>
<CommerceChangeDoubleTimes/>
<CommerceModifiers/>
<GlobalCommerceModifiers/>
<SpecialistExtraCommerces/>
<StateReligionCommerces/>
<CommerceHappinesses/>
<ReligionChanges/>
<SpecialistCounts/>
<FreeSpecialistCounts/>
<CommerceFlexibles/>
<CommerceChangeOriginalOwners/>
<ConstructSound/>
<BonusHealthChanges/>
<BonusHappinessChanges/>
<BonusProductionModifiers/>
<UnitCombatFreeExperiences/>
<DomainFreeExperiences/>
<DomainProductionModifiers/>
<BuildingHappinessChanges/>
<PrereqBuildingClasses/>
<BuildingClassNeededs/>
<SpecialistYieldChanges/>
<BonusYieldModifiers/>
<Flavors/>
<HotKey/>
<bAltDown>0</bAltDown>
<bShiftDown>0</bShiftDown>
<bCtrlDown>0</bCtrlDown>
<iHotKeyPriority>0</iHotKeyPriority>
</BuildingInfo>



This gives us a building that provides no bonuses to anything.

Next I create the replacement buildings for the heroic epic, in this case The Alamo. Again in C:\Program Files\Firaxis Games\Sid Meier's Civilization 4\Mods\Texas\Assets\XML\Buildings\CIV4BuildingClas sInfos.xml

The entry is as follows:
<BuildingClassInfo>
<Type>BUILDINGCLASS_THE_ALAMO</Type>
<Description>The Alamo</Description>
<iMaxGlobalInstances>-1</iMaxGlobalInstances>
<iMaxTeamInstances>-1</iMaxTeamInstances>
<iMaxPlayerInstances>1</iMaxPlayerInstances>
<iExtraPlayerInstances>0</iExtraPlayerInstances>
<bNoLimit>0</bNoLimit>
<DefaultBuilding>BUILDING_THE_ALAMO</DefaultBuilding>
<VictoryThresholds/>
</BuildingClassInfo>

and then create the building's entry in C:\Program Files\Firaxis Games\Sid Meier's Civilization 4\Mods\Texas\Assets\XML\Buildings\CIV4BuildingInfo s.xml
The entry is as follows
<BuildingInfo>
<BuildingClass>BUILDINGCLASS_THE_ALAMO</BuildingClass>
<Type>BUILDING_THE_ALAMO</Type>
<SpecialBuildingType>NONE</SpecialBuildingType>
<Description>The Alamo</Description>
<Civilopedia>TXT_KEY_BUILDING_THE_ALAMO_PEDIA</Civilopedia>
<Strategy>TXT_KEY_BUILDING_HEROIC_EPIC_STRATEGY</Strategy>
<Advisor>ADVISOR_MILITARY</Advisor>
<ArtDefineTag>ART_DEF_BUILDING_ALAMO</ArtDefineTag>
<MovieDefineTag>NONE</MovieDefineTag>
<HolyCity>NONE</HolyCity>
<ReligionType>NONE</ReligionType>
<StateReligion>NONE</StateReligion>
<PrereqReligion>NONE</PrereqReligion>
<GlobalReligionCommerce>NONE</GlobalReligionCommerce>
<VictoryPrereq>NONE</VictoryPrereq>
<FreeStartEra>NONE</FreeStartEra>
<MaxStartEra>ERA_RENAISSANCE</MaxStartEra>
<ObsoleteTech>NONE</ObsoleteTech>
<PrereqTech>TECH_LITERATURE</PrereqTech>
<TechTypes/>
<Bonus>NONE</Bonus>
<PrereqBonuses/>
<ProductionTraits/>
<PowerBonus>NONE</PowerBonus>
<FreeBonus>NONE</FreeBonus>
<iNumFreeBonuses>0</iNumFreeBonuses>
<FreeBuilding>NONE</FreeBuilding>
<FreePromotion>NONE</FreePromotion>
<CivicOption>NONE</CivicOption>
<GreatPeopleUnitClass>UNITCLASS_ARTIST</GreatPeopleUnitClass>
<iGreatPeopleRateChange>1</iGreatPeopleRateChange>
<bTeamShare>0</bTeamShare>
<bWater>0</bWater>
<bRiver>0</bRiver>
<bPower>0</bPower>
<bDirtyPower>0</bDirtyPower>
<bAreaCleanPower>0</bAreaCleanPower>
<bDiploVote>0</bDiploVote>
<bForceTeamVoteEligible>0</bForceTeamVoteEligible>
<bCapital>0</bCapital>
<bGovernmentCenter>0</bGovernmentCenter>
<bGoldenAge>0</bGoldenAge>
<bMapCentering>0</bMapCentering>
<bNoUnhappiness>0</bNoUnhappiness>
<bNoUnhealthyPopulation>0</bNoUnhealthyPopulation>
<bBuildingOnlyHealthy>0</bBuildingOnlyHealthy>
<bNeverCapture>0</bNeverCapture>
<bNukeImmune>0</bNukeImmune>
<bPrereqReligion>0</bPrereqReligion>
<bCenterInCity>0</bCenterInCity>
<iAIWeight>0</iAIWeight>
<iCost>200</iCost>
<iHurryCostModifier>50</iHurryCostModifier>
<iMinAreaSize>-1</iMinAreaSize>
<iConquestProb>0</iConquestProb>
<iCitiesPrereq>0</iCitiesPrereq>
<iTeamsPrereq>0</iTeamsPrereq>
<iLevelPrereq>4</iLevelPrereq>
<iMinLatitude>0</iMinLatitude>
<iMaxLatitude>90</iMaxLatitude>
<iGreatPeopleRateModifier>0</iGreatPeopleRateModifier>
<iGlobalGreatPeopleRateModifier>0</iGlobalGreatPeopleRateModifier>
<iAnarchyModifier>0</iAnarchyModifier>
<iGlobalHurryModifier>0</iGlobalHurryModifier>
<iExperience>0</iExperience>
<iGlobalExperience>0</iGlobalExperience>
<iFoodKept>0</iFoodKept>
<iAirlift>0</iAirlift>
<iAirModifier>0</iAirModifier>
<iNukeModifier>0</iNukeModifier>
<iNukeExplosionRand>0</iNukeExplosionRand>
<iFreeSpecialist>0</iFreeSpecialist>
<iAreaFreeSpecialist>0</iAreaFreeSpecialist>
<iGlobalFreeSpecialist>0</iGlobalFreeSpecialist>
<iMaintenanceModifier>0</iMaintenanceModifier>
<iWarWearinessModifier>0</iWarWearinessModifier>
<iGlobalWarWearinessModifier>0</iGlobalWarWearinessModifier>
<iHealRateChange>0</iHealRateChange>
<iHealth>0</iHealth>
<iAreaHealth>0</iAreaHealth>
<iGlobalHealth>0</iGlobalHealth>
<iHappiness>0</iHappiness>
<iAreaHappiness>0</iAreaHappiness>
<iGlobalHappiness>0</iGlobalHappiness>
<iStateReligionHappiness>0</iStateReligionHappiness>
<iWorkerSpeedModifier>0</iWorkerSpeedModifier>
<iMilitaryProductionModifier>100</iMilitaryProductionModifier>
<iSpaceProductionModifier>0</iSpaceProductionModifier>
<iGlobalSpaceProductionModifier>0</iGlobalSpaceProductionModifier>
<iTradeRoutes>0</iTradeRoutes>
<iCoastalTradeRoutes>0</iCoastalTradeRoutes>
<iGlobalTradeRoutes>0</iGlobalTradeRoutes>
<iTradeRouteModifier>0</iTradeRouteModifier>
<iGlobalPopulationChange>0</iGlobalPopulationChange>
<iFreeTechs>0</iFreeTechs>
<iDefense>0</iDefense>
<iAllCityDefense>0</iAllCityDefense>
<iAsset>8</iAsset>
<iPower>8</iPower>
<fVisibilityPriority>1.0</fVisibilityPriority>
<SeaPlotYieldChanges/>
<GlobalSeaPlotYieldChanges/>
<YieldChanges/>
<CommerceChanges/>
<ObsoleteSafeCommerceChanges>
<iCommerce>0</iCommerce>
<iCommerce>0</iCommerce>
<iCommerce>4</iCommerce>
</ObsoleteSafeCommerceChanges>
<CommerceChangeDoubleTimes>
<iCommerce>0</iCommerce>
<iCommerce>0</iCommerce>
<iCommerce>1000</iCommerce>
</CommerceChangeDoubleTimes>
<CommerceModifiers/>
<GlobalCommerceModifiers/>
<SpecialistExtraCommerces/>
<StateReligionCommerces/>
<CommerceHappinesses/>
<ReligionChanges/>
<SpecialistCounts/>
<FreeSpecialistCounts/>
<CommerceFlexibles/>
<CommerceChangeOriginalOwners/>
<ConstructSound/>
<BonusHealthChanges/>
<BonusHappinessChanges/>
<BonusProductionModifiers>
<BonusProductionModifier>
<BonusType>BONUS_STONE</BonusType>
<iProductonModifier>100</iProductonModifier>
</BonusProductionModifier>
</BonusProductionModifiers>
<UnitCombatFreeExperiences/>
<DomainFreeExperiences/>
<DomainProductionModifiers/>
<BuildingHappinessChanges/>
<PrereqBuildingClasses>
<PrereqBuildingClass>
<BuildingClassType>BUILDINGCLASS_TEXAS</BuildingClassType>
<iNumBuildingNeeded>1</iNumBuildingNeeded>
</PrereqBuildingClass>
</PrereqBuildingClasses>
<BuildingClassNeededs>
<BuildingClassNeeded>
<BuildingClassType>BUILDINGCLASS_BARRACKS</BuildingClassType>
<bNeededInCity>1</bNeededInCity>
</BuildingClassNeeded>
</BuildingClassNeededs>
<SpecialistYieldChanges/>
<BonusYieldModifiers/>
<Flavors>
<Flavor>
<FlavorType>FLAVOR_MILITARY</FlavorType>
<iFlavor>10</iFlavor>
</Flavor>
</Flavors>
<HotKey/>
<bAltDown>0</bAltDown>
<bShiftDown>0</bShiftDown>
<bCtrlDown>0</bCtrlDown>
<iHotKeyPriority>0</iHotKeyPriority>
</BuildingInfo>


This entry is identical to the original heroic epic in terms of requirements and bonuses, except it has the addition of a prerequisite building class.

Next I create the Natonal Epic for the civ in the same way as I did the heroic epic, using the National Epic entry as the base and adding the prerequisite building code to it. Next I add the civlopedia entries in C:\Program Files\Firaxis Games\Sid Meier's Civilization 4\Mods\Texas\Assets\XML\Text\CIV4GameText_Civilope dia_BuildingsProjects.xml

The generic format is as follows:

<TEXT>
<Tag>TXT_KEY_BUILDING_YOURBUILDINGNAME_PEDIA</Tag>
<English>[TAB]YOUR DESCRIPTION FOR THE CIVLOPEDIA
</English>
</TEXT>


If you are multilingual you can also add descriptions in one of the other available languages. PLEASE NOTE: for every building you referenced using the civlopedia key example: <Civilopedia>TXT_KEY_BUILDING_THE_ALAMO_PEDIA</Civilopedia>
you need to create the above entry, (although you can leave everything between <English> and </English> blank if you don't want a description. Make sure the <Tag> entry is the same as the <Civlopedia> entry.

Next I create the buttons for the civopedia (see the adding a new civ mod on how to dreate buttons) and add the art entries to the C:\Program Files\Firaxis Games\Sid Meier's Civilization 4\Mods\Texas\Assets\XML\Art\CIV4ArtDefines_Buildin g.xml file

for the alamo I am creating a new model so it's entry reads as <BuildingArtInfo>
<Type>ART_DEF_BUILDING_ALAMO</Type>
<bAnimated>0</bAnimated>
<fScale>0.7</fScale>
<fInterfaceScale>0.7</fInterfaceScale>
<NIF>Art/Structures/Buildings/Alamo/Alamo.nif</NIF>
<KFM/>
<Button>,Art/Interface/Buttons/Buildings/Alamo.dds</Button>
</BuildingArtInfo>


if you can't create a model or don't need to (my national epic is san jacinto battlefield, which in real life is marked by an obelisk so I just use that model.)
You can copy an existing model to the folder you pointed to in the <NIF> entry. in this case C:\Program Files\Firaxis Games\Sid Meier's Civilization 4\Mods\Texas\Assets\Art\structures\buildings\Alamo
You can probably just point the <NIF> entry to an existing model in the original install path instead of having to make a copy of the model.

Finally we need to edit the C:\Program Files\Firaxis Games\Sid Meier's Civilization 4\Mods\Texas\Assets\XML\Civilizations\CIV4Civiliza tionInfos.xml file so we can use these new buildings the whole entry for my civ is as follows:
<CivilizationInfo>
<Type>CIVILIZATION_TEXAS</Type>
<Description>The Republic of Texas</Description>
<ShortDescription>Texas</ShortDescription>
<Adjective>Texan</Adjective>
<Civilopedia>TXT_KEY_CIV_TEXAS_PEDIA</Civilopedia>
<DefaultPlayerColor>PLAYERCOLOR_NAVY</DefaultPlayerColor>
<ArtDefineTag>ART_DEF_CIVILIZATION_TEXAS</ArtDefineTag>
<ArtStyleType>ARTSTYLE_EUROPEAN</ArtStyleType>
<bPlayable>1</bPlayable>
<bAIPlayable>1</bAIPlayable>
<Cities>
<City>Austin</City>
<City>Dallas</City>
<City>Houston</City>
<City>San Antonio</City>
<City>Fort Worth</City>
<City>Abiliene</City>
<City>Killeen</City>
<City>Waco</City>
<City>Tyler</City>
<City>Big Springs</City>
<City>San Angelo</City>
<City>Corpus Christi</City>
<City>Del Rio</City>
<City>Nacogdoches</City>
<City>El Dorado</City>
<City>Pflugerville</City>
<City>Fort Stockton</City>
<City>San Marcos</City>
<City>Amarillo</City>
<City>Brownwood</City>
<City>El Paso</City>
<City>Uvalde</City>
<City>Round Rock</City>
<City>Plano</City>
<City>Red Rock</City>
<City>Mesquite</City>
<City>Midland</City>
<City>Odessa</City>
<City>Lubbock</City>
<City>Richardson</City>
<City>Kerville</City>
<City>Fredericksburg</City>
<City>New Brausfels</City>
<City>Arlington</City>
<City>College Station</City>
<City>Denton</City>
<City>Wichita Falls</City>
<City>Harlingen</City>
<City>Galveston</City>
<City>Jasper</City>
<City>Irving</City>
<City>Katy</City>
<City>Bryan</City>
<City>Justin</City>
<City>Beaumont</City>
<City>Grapevine</City>
<City>Shamrock</City>
<City>Rock Springs</City>
<City>Copperas Cove</City>
<City>Wylie</City>
</Cities>
<Buildings>
<Building>
<BuildingClassType>BUILDINGCLASS_HEROIC_EPIC</BuildingClassType>
<BuildingType>NONE</BuildingType>
</Building>
<Building>
<BuildingClassType>BUILDINGCLASS_NATIONAL_EPIC</BuildingClassType>
<BuildingType>NONE</BuildingType>
</Building>
</Buildings>
<Units>
<Unit>
<UnitClassType>UNITCLASS_CAVALRY</UnitClassType>
<UnitType>UNIT_TEXAS_RANGER</UnitType>
</Unit>
</Units>
<FreeUnitClasses>
<FreeUnitClass>
<UnitClassType>UNITCLASS_SETTLER</UnitClassType>
<iFreeUnits>1</iFreeUnits>
</FreeUnitClass>
</FreeUnitClasses>
<FreeBuildingClasses>
<FreeBuildingClass>
<BuildingClassType>BUILDINGCLASS_TEXAS</BuildingClassType>
<bFreeBuildingClass>1</bFreeBuildingClass>
</FreeBuildingClass>
<FreeBuildingClass>
<BuildingClassType>BUILDINGCLASS_PALACE</BuildingClassType>
<bFreeBuildingClass>1</bFreeBuildingClass>
</FreeBuildingClass>
</FreeBuildingClasses>
<FreeTechs>
<FreeTech>
<TechType>TECH_AGRICULTURE</TechType>
<bFreeTech>1</bFreeTech>
</FreeTech>
<FreeTech>
<TechType>TECH_HUNTING</TechType>
<bFreeTech>1</bFreeTech>
</FreeTech>
</FreeTechs>
<DisableTechs/>
<InitialCivics>
<CivicType>CIVIC_DESPOTISM</CivicType>
<CivicType>CIVIC_BARBARISM</CivicType>
<CivicType>CIVIC_TRIBALISM</CivicType>
<CivicType>CIVIC_DECENTRALIZATION</CivicType>
<CivicType>CIVIC_PAGANISM</CivicType>
</InitialCivics>
<AnarchyCivics>
<CivicType>CIVIC_DESPOTISM</CivicType>
<CivicType>CIVIC_BARBARISM</CivicType>
<CivicType>CIVIC_TRIBALISM</CivicType>
<CivicType>CIVIC_DECENTRALIZATION</CivicType>
<CivicType>CIVIC_PAGANISM</CivicType>
</AnarchyCivics>
<Leaders>
<Leader>
<LeaderName>LEADER_HOUSTON</LeaderName>
<bLeaderAvailability>1</bLeaderAvailability>
</Leader>
<Leader>
<LeaderName>LEADER_AUSTIN</LeaderName>
<bLeaderAvailability>1</bLeaderAvailability>
</Leader>
</Leaders>
<CivilizationSelectionSound>AS3D_AMERICA_SELECT</CivilizationSelectionSound>
<CivilizationActionSound>AS3D_AMERICA_ORDER</CivilizationActionSound>
</CivilizationInfo>


The important areas for our purposes are the <Buildings>
<Building>
<BuildingClassType>BUILDINGCLASS_HEROIC_EPIC</BuildingClassType>
<BuildingType>NONE</BuildingType>
</Building>
<Building>
<BuildingClassType>BUILDINGCLASS_NATIONAL_EPIC</BuildingClassType>
<BuildingType>NONE</BuildingType>
</Building>
</Buildings> entries which disable our civ from building the default national and heroic epics and the <FreeBuildingClasses>
<FreeBuildingClass>
<BuildingClassType>BUILDINGCLASS_TEXAS</BuildingClassType>
<bFreeBuildingClass>1</bFreeBuildingClass>
</FreeBuildingClass>
<FreeBuildingClass>
<BuildingClassType>BUILDINGCLASS_PALACE</BuildingClassType>
<bFreeBuildingClass>1</bFreeBuildingClass>
</FreeBuildingClass>
</FreeBuildingClasses>
entries, this grants our new cultural building in addition to the palace when we build our first city.

NOTE: There are still a couple of areas that need to be addressed,

1st on huge maps only none of this works as the game for some reason requires 2 instances of our civ specific building instead of 1 so you can't build the heroic or national epic.

2nd I don't know what happens if your first city is lost as I haven't play tested that yet.

Anyhow, that's how I created a civ specific national epic and heroic epic. Hopefully there aren't any typos in the important parts of these instructions.