The following shows the XML for loading the Battle Ready class feature in to the offline Character Builder.  And yup it works 

 it also takes a modification of the base class. 
<RulesElement name ="Battle Ready" type="Class Feature" internal-id="ID_LAD_CLASS_FEATURE_BR1234" source="Martial Power III" revision-date="6/16/2019" >
   <Flavor>Most people react to the onset of a fight for you it is always part of the plan.</Flavor>
   <Prereqs> Fighter </Prereqs>
        <print-prereqs> Fighter </print-prereqs>
        <specific name="Tier"> Heroic </specific>
        <specific name="Short Description"> You may substitute Mental Attributes for Dexterity in Initiative </specific>
        <specific name="Special" />
        <specific name="type" />
        <specific name="Associated Power Info" />
        <specific name="Associated Powers" />
        <rules>
            <statadd name="Initiative" value="+Intelligence modifier" type="Ability" />
            <statadd name="Initiative" value="+Wisdom modifier" type="Ability" />
            <statadd name="Initiative" value="+Charisma modifier" type="Ability" /> 
        </rules>
You may use your Intelligence, Wisdom, Charisma or Dexterity modifier when rolling initiative. 
   </RulesElement>