Mod Cooperative

So I have a small gpsl with a niche interest (would rather not go further into detail on what it is). Long story short, there's a particular player with said niche interest who ragequit the game a while back. However, they are trying to come back, again and again, with new characters. To the point of asking for lines against players that they have antagonized and hurt in the past while pretending to be a completely different player, or at least not disclosing that they are the player from before.

I don't know what to do. We basically allow everyone in who applies. I can't think of a good reason to refuse them membership.

Does anyone have any ideas on how to handle this issue?