You'll have to contact Gstaff for any minor changes to your username. Just send him a PM and you should receive a reply within in a couple of weeks, with your request in effect.
Only if you're lucky. I asked him to change my name to "Magical Steve the fire-breathing black hole", but he didn't go for it, and that's virtually identical to my current username
I thought any mod would do. :/
Only admins have the ability to change usernames