Hey i actuallyu found a semi solve to this problem myself, but im not sure if its the correct way to go about it, but it works pretty effectivly...
Only thing is youll need microsoft visual studio, or another program capable of editing files in this manner.
Its pretty simple though, once you have visual studio or another such program, you can open up the worldbuilder save in a text format, and edit pretty much anything you want from there.
Its pretty simple, but you cant add extra civs, you have to keep the number of civilizations at the same number.
Anyways youll see something like this....
"Version=11
BeginGame
Era=ERA_ANCIENT
Speed=GAMESPEED_EPIC
Calendar=CALENDAR_DEFAULT
Victory=VICTORY_TIME
Victory=VICTORY_CONQUEST
Victory=VICTORY_DOMINATION
Victory=VICTORY_CULTURAL
Victory=VICTORY_SPACE_RACE
Victory=VICTORY_DIPLOMATIC
GameTurn=0
MaxTurns=1000
MaxCityElimination=0
NumAdvancedStartPoints=0
TargetScore=0
StartYear=-4000
Description=
ModPath=
EndGame
BeginTeam
TeamID=0
Tech=TECH_FISHING
Tech=TECH_AGRICULTURE
ContactWithTeam=0
RevealMap=0"
(Thats just the 1st couple of lines...) To edit and change the civs you simply need to choose a civ you want to remove.... so for my example....
"BeginTeam
TeamID=1
Tech=TECH_MYSTICISM
Tech=TECH_THE_WHEEL
ContactWithTeam=1
RevealMap=0
EndTeam"
Further down youll find the relating info for this team....
"BeginPlayer
Team=1
LeaderType=LEADER_SALADIN
LeaderName=Saladin
CivDesc=Arabian Empire
CivShortDesc=Arabia
CivAdjective=Arabian
FlagDecal=Art/Interface/TeamColor/FlagDECAL_Arabic.dds
WhiteFlag=0
CivType=CIVILIZATION_ARABIA
Color=PLAYERCOLOR_DARK_GREEN
ArtStyle=ARTSTYLE_MIDDLE_EAST
PlayableCiv=1
MinorNationStatus=0
StartingGold=0
StartingX=107, StartingY=85
StateReligion=
StartingEra=ERA_ANCIENT
RandomStartLocation=false
CivicOption=CIVICOPTION_GOVERNMENT, Civic=CIVIC_DESPOTISM
CivicOption=CIVICOPTION_LEGAL, Civic=CIVIC_BARBARISM
CivicOption=CIVICOPTION_LABOR, Civic=CIVIC_TRIBALISM
CivicOption=CIVICOPTION_ECONOMY, Civic=CIVIC_DECENTRALIZATION
CivicOption=CIVICOPTION_RELIGION, Civic=CIVIC_PAGANISM
Handicap=HANDICAP_NOBLE
EndPlayer"
These are the two set of lines which you will have to modify to choose a new civ
Choose the civ you want to replace it with, and then go into your CIV4civilizationinfos.xml file, found in assets> xml,> civilizations in either your CIV4 or CIV4 warlors / and or Beyond the sword base folder
then simply swap the details you find in there, in place of the original text that you find
BeginPlayer
Team=1
LeaderType=LEADER_SALADIN
LeaderName=Saladin
CivDesc=Chinese Empire
CivShortDesc=China
CivAdjective=Chinese
FlagDecal=Art/Interface/TeamColor/FlagDECAL_Dragon.dds
WhiteFlag=0
CivType=CIVILIZATION_CHINA
Color=PLAYERCOLOR_DARK_PINK
ArtStyle=ARTSTYLE_ASIAN
PlayableCiv=1
MinorNationStatus=0
StartingGold=0
StartingX=107, StartingY=85
StateReligion=
StartingEra=ERA_ANCIENT
RandomStartLocation=false
CivicOption=CIVICOPTION_GOVERNMENT, Civic=CIVIC_DESPOTISM
CivicOption=CIVICOPTION_LEGAL, Civic=CIVIC_BARBARISM
CivicOption=CIVICOPTION_LABOR, Civic=CIVIC_TRIBALISM
CivicOption=CIVICOPTION_ECONOMY, Civic=CIVIC_DECENTRALIZATION
CivicOption=CIVICOPTION_RELIGION, Civic=CIVIC_PAGANISM
Handicap=HANDICAP_NOBLE
EndPlayer
So as you can see i choose China, but you wont get your leader info from that civ4 xml, so you need to go into your civ4leaderheadinfo.xml folder, found in the same place, and fill in the rest of the info about the leader
BeginPlayer
Team=1
LeaderType=LEADER_CHINESE_LEADER
LeaderName=Mao Zedong
CivDesc=Chinese Empire
Then make sure you have the correcr techs added.... so go back into your civ4civilizationinfos.xml file.... and swap the test correctly here...
BeginTeam BeginTeam
TeamID=1 TeamID=1
Tech=TECH_MYSTICISM Tech=TECH_AGRICULTURE
Tech=TECH_THE_WHEEL Tech=MINIG
ContactWithTeam=1
RevealMap=0
EndTeam
Now when you save that, assuming everything was done correctly, and you havnt deleted anything, you should be able to load up the game with your new player, and you will start where the old player began. To modify that, load up the game and play as the 1st civ so that none of the players can begin their turn. And then enter the world builder.
Place a settler and a scout / or warrior, depending on which your player recieves, where you want them to begin, and then delete the old ones, save, and restart. Simple as that. Now you will start where you want, with your new civ.
The only downside is you will have a fogged, revealed set of map tiles, 4x4 where your old player started. But you wont be able to see anything so its really not a big deal.
Anyways hope that at least points you in the right direction. Its a pretty horsehockey guide but it should give you an idea. IF you dont have visual studio, look on the forums for alternative SDK editing tools, and follow the instructions.