As per the attached picture, modding the Explorer progression. I can't find the default defined anywhere, and the unit's art info defines the image successfully.
Click for full size.
---------------------------------------------------------------------------
My modded Explorer data:

Click for full size.
---------------------------------------------------------------------------
My modded Explorer data:
Code:
<?xml version="1.0" encoding="utf-8"?>
<!-- edited with XMLSPY v2004 rel. 2 U (http://www.xmlspy.com) by Anton Strenger (Firaxis Games) -->
<GameData>
<Units>
<Update>
<Set Moves="2" />
<Where Type="UNIT_EXPLORER" />
</Update>
<Update>
<Set Combat="8" />
<Where Type="UNIT_EXPLORER" />
</Update>
</Units>
<UnitUpgrades>
<Row>
<Type>UNITUPGRADE_EXPLORER_1</Type>
<Description>Hardened Explorer</Description>
<UnitType>UNIT_EXPLORER</UnitType>
<UpgradeTier>1</UpgradeTier>
<AnyAffinityLevel>1</AnyAffinityLevel>
<ExtraProductionCost>10</ExtraProductionCost>
<FreePerk>UNITPERK_MARINE_1</FreePerk>
<IconAtlas>UNIT_UPGRADE_ATLAS_1</IconAtlas>
<PortraitIndex>2</PortraitIndex>
</Row>
<Row>
<Type>UNITUPGRADE_EXPLORER_2H</Type>
<Description>TXT_KEY_UNIT_MARINE03H</Description>
<UnitType>UNIT_EXPLORER</UnitType>
<UpgradeTier>2</UpgradeTier>
<HarmonyLevel>3</HarmonyLevel>
<ExtraProductionCost>10</ExtraProductionCost>
<FreePerk>UNITPERK_MARINE_2H</FreePerk>
<IconAtlas>UNIT_UPGRADE_ATLAS_1</IconAtlas>
<PortraitIndex>2</PortraitIndex>
</Row>
<Row>
<Type>UNITUPGRADE_EXPLORER_2P</Type>
<Description>TXT_KEY_UNIT_MARINE03P</Description>
<UnitType>UNIT_EXPLORER</UnitType>
<UpgradeTier>2</UpgradeTier>
<PurityLevel>3</PurityLevel>
<ExtraProductionCost>10</ExtraProductionCost>
<FreePerk>UNITPERK_MARINE_2P</FreePerk>
<IconAtlas>UNIT_UPGRADE_ATLAS_1</IconAtlas>
<PortraitIndex>2</PortraitIndex>
</Row>
<Row>
<Type>UNITUPGRADE_EXPLORER_2S</Type>
<Description>TXT_KEY_UNIT_MARINE03S</Description>
<UnitType>UNIT_EXPLORER</UnitType>
<UpgradeTier>2</UpgradeTier>
<SupremacyLevel>3</SupremacyLevel>
<ExtraProductionCost>10</ExtraProductionCost>
<FreePerk>UNITPERK_MARINE_2S</FreePerk>
<IconAtlas>UNIT_UPGRADE_ATLAS_1</IconAtlas>
<PortraitIndex>2</PortraitIndex>
</Row>
<Row>
<Type>UNITUPGRADE_EXPLORER_3H</Type>
<Description>TXT_KEY_UNIT_MARINE04H</Description>
<UnitType>UNIT_EXPLORER</UnitType>
<UpgradeTier>3</UpgradeTier>
<HarmonyLevel>5</HarmonyLevel>
<ExtraProductionCost>10</ExtraProductionCost>
<FreePerk>UNITPERK_MARINE_3H</FreePerk>
<IconAtlas>UNIT_UPGRADE_ATLAS_1</IconAtlas>
<PortraitIndex>2</PortraitIndex>
</Row>
<Row>
<Type>UNITUPGRADE_EXPLORER_3P</Type>
<Description>TXT_KEY_UNIT_MARINE04P</Description>
<UnitType>UNIT_EXPLORER</UnitType>
<UpgradeTier>3</UpgradeTier>
<PurityLevel>5</PurityLevel>
<ExtraProductionCost>10</ExtraProductionCost>
<FreePerk>UNITPERK_MARINE_3P</FreePerk>
<IconAtlas>UNIT_UPGRADE_ATLAS_1</IconAtlas>
<PortraitIndex>2</PortraitIndex>
</Row>
<Row>
<Type>UNITUPGRADE_EXPLORER_3S</Type>
<Description>TXT_KEY_UNIT_MARINE04S</Description>
<UnitType>UNIT_EXPLORER</UnitType>
<UpgradeTier>3</UpgradeTier>
<SupremacyLevel>5</SupremacyLevel>
<ExtraProductionCost>10</ExtraProductionCost>
<FreePerk>UNITPERK_MARINE_3S</FreePerk>
<IconAtlas>UNIT_UPGRADE_ATLAS_1</IconAtlas>
<PortraitIndex>2</PortraitIndex>
</Row>
</UnitUpgrades>
<UnitUpgradePerkChoices>
<Row>
<UpgradeType>UNITUPGRADE_EXPLORER_1</UpgradeType>
<PerkType>UNITPERK_ATTACK_0</PerkType>
</Row>
<Row>
<UpgradeType>UNITUPGRADE_EXPLORER_1</UpgradeType>
<PerkType>UNITPERK_DAMAGE_ON_DEATH</PerkType>
</Row>
<Row>
<UpgradeType>UNITUPGRADE_EXPLORER_2H</UpgradeType>
<PerkType>UNITPERK_HEALING_1</PerkType>
</Row>
<Row>
<UpgradeType>UNITUPGRADE_EXPLORER_2H</UpgradeType>
<PerkType>UNITPERK_DEFEND_2</PerkType>
</Row>
<Row>
<UpgradeType>UNITUPGRADE_EXPLORER_2S</UpgradeType>
<PerkType>UNITPERK_HEALING_1</PerkType>
</Row>
<Row>
<UpgradeType>UNITUPGRADE_EXPLORER_2S</UpgradeType>
<PerkType>UNITPERK_DEFEND_2</PerkType>
</Row>
<Row>
<UpgradeType>UNITUPGRADE_EXPLORER_2P</UpgradeType>
<PerkType>UNITPERK_HEALING_1</PerkType>
</Row>
<Row>
<UpgradeType>UNITUPGRADE_EXPLORER_2P</UpgradeType>
<PerkType>UNITPERK_DEFEND_2</PerkType>
</Row>
<Row>
<UpgradeType>UNITUPGRADE_EXPLORER_3H</UpgradeType>
<PerkType>UNITPERK_STRONGER_NOT_ADJACENT_TO_FRIENDLY_1</PerkType>
</Row>
<Row>
<UpgradeType>UNITUPGRADE_EXPLORER_3H</UpgradeType>
<PerkType>UNITPERK_ALWAYS_HEAL</PerkType>
</Row>
<Row>
<UpgradeType>UNITUPGRADE_EXPLORER_3S</UpgradeType>
<PerkType>UNITPERK_STRONGER_NOT_ADJACENT_TO_FRIENDLY_1</PerkType>
</Row>
<Row>
<UpgradeType>UNITUPGRADE_EXPLORER_3S</UpgradeType>
<PerkType>UNITPERK_ALWAYS_HEAL</PerkType>
</Row>
<Row>
<UpgradeType>UNITUPGRADE_EXPLORER_3P</UpgradeType>
<PerkType>UNITPERK_STRONGER_NOT_ADJACENT_TO_FRIENDLY_1</PerkType>
</Row>
<Row>
<UpgradeType>UNITUPGRADE_EXPLORER_3P</UpgradeType>
<PerkType>UNITPERK_ALWAYS_HEAL</PerkType>
</Row>
</UnitUpgradePerkChoices>
</GameData>