This is a good idea, but with a 30d cool down, like Mojang. I think it needs a cool down because some people would definitely abuse this with changing their forum names all the time. But this is a good suggestion, I like it.
*Edit* Or Admins/Mods could be able to change our names instead, also to prevent players abusing the idea.
Well I say this as then everyone what's the point of buying perks for ranks, I see why it's fair to give to everyone, but I also want something on the forums as ranks don't get a lot on here except signatures and titles, I'm willing to say have Iron ranks even to change their names, but diamond+ should have more perms overall for spending money on the server.