Modifying core elements

Greetings

simple question:

I want to restrict certain core elements (spells, items, abilities, etc) to custom factions. I know how to do this, What I don't know is:

Is it best to copy the core element into my mods xmls in its entirety or or just the identifier and the elements I want to add, change or remove?

example:

    <AbilityBonus InternalName="AcrobatAbility">

     <AbilityBonusType>Unit_Design</AbilityBonusType>

      <AbilityBonusOption InternalName="Acrobat">

            <DisplayName>Acrobat</DisplayName>

             <Description>+1 Dodge per Level</Description>

             <Icon>Ability_Acrobat_Icon.png</Icon>

         <Prereq>     

 <Type>RestrictedAbilityBonusOption</Type>        

<Target>Player</Target>              

 <Attribute>my_custom_junk_here</Attribute>        

 </Prereq>            

<GameModifier>                

<ModType>Unit</ModType>                

 <Attribute>AdjustUnitStat</Attribute>                

 <StrVal>UnitStat_Dodge</StrVal>                

 <Value>1</Value>                

 <PerLevel>1</PerLevel>                

<Provides>+1 Dodge per Level</Provides>            

 </GameModifier>            

<AdditionalTrainingTurns>6</AdditionalTrainingTurns>            

 <HideWhenUpgraded>0</HideWhenUpgraded>            

 <Type>Defensive</Type>            

<AIData AIPersonality="AI_General">                

 <AIPriority>5</AIPriority>            

</AIData>        

 </AbilityBonusOption>    

</AbilityBonus>

Or this:

    <AbilityBonus InternalName="AcrobatAbility">

         <AbilityBonusType>Unit_Design</AbilityBonusType>

         <AbilityBonusOption InternalName="Acrobat">

         <Prereq>

      <Type>RestrictedAbilityBonusOption</Type>

         <Target>Player</Target>

               <Attribute>my_custom_junk_here</Attribute>

         </Prereq>

        </AbilityBonusOption>

     </AbilityBonus>

Or maybe both are wrong?

Edit:

Is there a risk of doubling gamemodifiers? From the above example; getting +2 dodge when it should be +1, +1 twice?