Hi.

CoreImprovements.xml is the file you need.

Here is the example for Binding (Resoln). Best thing to do would be to create a new Ability, new Improvements (shards) for that ability and connect that ability to the faction you want -> i.e. give the ability to the faction.

That way you wouldn't modify core game files.

    <ImprovementType InternalName="DeathShrine_Resoln">
        <DisplayName>Death Shrine</DisplayName>
        <Description>Death Shrines upgrade from Death Altars. They amplify Death spells and provide you with additional Mana every Season.</Description>
        <SpecialBuildingType>Shard</SpecialBuildingType>
        <IgnoreDuplicateImpLimit>1</IgnoreDuplicateImpLimit>
        <RequiresCity>0</RequiresCity>
        <RequiresResource>1</RequiresResource>
        <SupportedResourceType>DeathShard</SupportedResourceType>
        <PreferredTerrain>Category:Land</PreferredTerrain>
        <UpgradesToImprovement>DeathTemple_Resoln</UpgradesToImprovement>
        <UpgradeTier>2</UpgradeTier>
        <HideInHiergamenon>1</HideInHiergamenon>
        <Prereq>
            <Type>Allegiance</Type>
            <Attribute>Empire</Attribute>
        </Prereq>
        <Prereq>
            <Type>AbilityBonusOption</Type>
            <Attribute>Binding</Attribute>
            <Target>Player</Target>
        </Prereq>
        <Prereq>
            <Type>Tech</Type>
            <Attribute>Shard_Harvesting</Attribute>
        </Prereq>
        <LaborToBuild>166</LaborToBuild>
        <GameModifier>
            <ModType>Resource</ModType>
            <Attribute>Mana</Attribute>
            <Value>2</Value>
            <PerTurn>1</PerTurn>
            <Provides>+2 Mana</Provides>
            <UpgradeComparisonID>1</UpgradeComparisonID>
        </GameModifier>
        <GameModifier>
            <ModType>Resource</ModType>
            <Attribute>DeathMana</Attribute>
            <Value>1</Value>
            <PerTurn>1</PerTurn>
            <Provides>+1 Death Power</Provides>
            <UpgradeComparisonID>2</UpgradeComparisonID>
        </GameModifier>
        <GameModifier>
            <ModType>Player</ModType>
            <Attribute>LimitedUnitCap</Attribute>
            <StrVal>CyndrumDemon</StrVal>
            <Value>1</Value>
            <Provides>Summons a Cyndrum Demon</Provides>
        </GameModifier>
        <AIData AIPersonality="AI_General">
            <AIPriority>5</AIPriority>
            <AITag>Shards</AITag>
        </AIData>