I goofed and – thinking "oh the world will be blown away during these tests, so will my little character" – did not choose my usual username. Now I very much want to change it to MetaGrrrl, but it's not something that I can just change in my profile.
Here's where it gets complicated. I think it's good to have some consistent sense of identity, particularly when our appearances seem likely to be completely mutable. My hypothesis is that encourages better social behavior than effective anonymity. Sticking around with an account has the benefit of building up skills (power). To gain the freedom of not being associated with your past actions, you should have to pay a cost – starting over from square one with a new name. (Aside: Square One might be a nice place name).
But, we do go through change over time. People do change their main public handle out in the non-Glitch online world. Seems like we should want to support that, but in a way that doesn't damage the pattern above. How about if your profile also had a "Gossip" section?
"You know, before Turkmenbashi, year 8, she used to be called 'Hepsibah'."
"Check out these old pictures of her!"
"Striatic told me she mooned him. Can you believe it?"