One time name change

Short answer: No, pick a name that is suitable from the outset. If you make a silly name that you regret, that's on you, and you should have thought about it from the outset and made use of the /Lastname function a bit better instead

The long answer: This is currently at GM discretion for stepping outside of the normal policy which is the name you choose is the name you remain (unless of course a name breaches naming etiquette in which case a GM will kindly change it for you regardless, free of charge, no thanks required.) In some very fringe cases (evidence of excessive unwarranted bullying or some such extreme case where anonymity is justifiably requested) then it's possible a GM may be persuaded, however by policy allowing identity changes is a firm no - you don't get to steal your guild's vault contents in a fit of rage and then change your name to hide your identity within the game setting. That's just the first off-the-top-of-my-head scenario that springs to mind, no doubt there's dozens of other reasons that ill-wishing people could find to abuse an identity change, but I'm sure you take the meaning behind it.