I am pretty sure the only way to do that (in a sense) is to set up another account. You would have to make sure you didn't use the old one anymore though. I don't think there's anything wrong with your username at the moment?
Believe me, I've thought about it a thousand times. CHOOSE WISELY NEW USER you never know how involved you're going to become or how long you're going to be stuck with the first thing that comes into your head!
But words are things, and a small drop of ink, falling, like dew, upon a thought produces that which makes thousands, perhaps millions think and smile.
Art is everywhere, except it has to pass through a creative mind.
Thanks