Yeah, I used to have a beta tag on my username. As Tryxus said, send a ticket. There was an automated one time thing for players who were in the betas. But, that's about it.
I doubt you'll be able to get yours changed, even if you send in a ticket. Mine was changed when I rejoined the forums earlier this year, but only because I had an old randomly generated beta name that included part of my RL name. They made it clear to me that the name change would be a one-time deal.