Username changes can be done, though its not somethin' to make a practice of; the folks who pull the levers and push the buttons around here have other priorities more pressin' than helpin' somebody pick out a new outfit whenever the mood strikes.
The best way to start would be to submit a request usin' the form found by clicking the "Contact Us" link down at the bottom of every page, just below the line that says "The time now is ... " - to make it easier, you can click this link --->
Contact Us
That'll get your question right to the attention of folks who have the real answers about stuff havin' to do with the policy and proceedures of this website. Be patient - it might take a while to get a response, but you'll get one.