Apparently this happened back in February, but I didn't see anyone talk about it, so, uhh, yeah.
You can finally change your Code.org username.
From what I've seen, the restrictions are 5-20 characters, and lowercase letters, numbers, underscores, dashes, and periods. Profanity isn't allowed either. Sound familiar?
Usernames aren't used for anything other than logging in, and profanity is filtered out, so I don't understand why this change was made unless they plan on making usernames public in the future.