Bulbagarden gives everyone the option to change their own username. However, there is a wait time between changing from one name to the next so we don't put too much strain on server.
Admins (the only staff who can change usernames) have been happy to change a users's name when they mistakingly change it instead of their user title, for example. However, we would appreciate it if you only asked us to change your name because of an error you made with it, not to get around the wait period between name changes. This also eases confusion of other users who may lose track of what name you're going by.