There is something already with the internal name "AcrobatAbility_Level"
I recommend you use different internal names than what the program is using unless you plan on overwriting the coreability.xml
There is problems with the object sanity in this game. Somethings will be completely overwritten like units files and somethings that just combine together like abilities. So for here if you want to replace AcrobatAbility_Level to be able be selected at the beginning use
<container>
<AbilityBonus InternalName="AcrobatAbility_Champion">
<AbilityBonusType>Champion_Talent</AbilityBonusType>
<AbilityBonusOption InternalName="Acrobat_Champion">
<DisplayName>Acrobat</DisplayName>
<Description>+1 Dodge per Level</Description>
<Icon>Ability_Acrobat_Icon.png</Icon>
<GameModifier>
<ModType>Unit</ModType>
<Attribute>AdjustUnitStat</Attribute>
<StrVal>UnitStat_Dodge</StrVal>
<Value>1</Value>
<PerLevel>1</PerLevel>
<Provides>+1 Dodge per Level</Provides>
</GameModifier>
<Cost>1</Cost>
<HideWhenUpgraded>0</HideWhenUpgraded>
<Type>Defense</Type>
<AIData AIPersonality="AI_General">
<AIPriority>5</AIPriority>
</AIData>
</AbilityBonusOption>
</AbilityBonus>
</container>
If you don't want the ability to select it as a level up option then you will need to have
<AbilityBonus InternalName="AcrobatAbility_Level">
<AbilityBonusOption InternalName="Acrobat_Level">
<Prereq>
<Type>RestrictedAbilityBonusOption</Type>
<Attribute>Acrobat_Champion</Attribute>
<Target>Unit</Target>
</Prereq>
</AbilityBonusOption InternaName="Acrobat_Level">
</AbilityBonus>