(Sorry for my previous typo's... Freakin butter fingers here... jeesh)

The custom title is what shows under their Username OR display name if they have changed it.

I want to only allow certain groups to be able to change the display name that shows instead of their username if enabled. For instance, if someone subscribes to the site and gets set to the "Silver Members" group, they are allowed to change their display name. EG: My username is deejay23. If i wanted to change that I would go to my profile and change my display name to Deejay instead and it would show on my posts instead of deejay23.

I think you may be confusing the Display name with the custom user title?

When a user signs up they enter what they want for a username. If the site is set up to allow it, it also allows a Display name, which we have disabled/removed from the template in our case.

I wish to allow certain groups the ability to change their Display name. (They are already allowed to change their Title any time..)

Hope I clarified a little better? Maybe I am missing something but Im pretty sure i didnt see any way to do this?