The answer to my first question clears some things up for me. Thanks! For some reason, I thought the timeline this RP takes place sometime after the effects of the mirror/Kayaba's announcement and that we'll only get to do hair color/clothing changes.

As for the kind of changes I was thinking about... I'm considering applying for a young character that's about 12-13 years old. For the start of the game, I thought it would be fun to have them hide behind an avatar that looks far older than their RL self. Would that be possible?