Replacing Username with Custom Field


Was curious on the difficulty of replacing the Username with a Custom Field in a site-wide fashion. I'm currently using XenForo as an Enjin replacement for a gaming group. A nice-to-have that my users have asked for is the ability to have a username/login different from their in-game character names.

I know I can go the brute-force method of add the prepare statement to a lot of the PHP back-end and then do a search for every instance of $user in the templates and modify if necessary; but that's a lot of work.

Anyone got an alternative idea/approach to this?