Once the name is determined, it can't be changed. GUEST does not seem to be an illegal name. I'm not sure if you can change your name from Bay Shore 3 to Bay Shore 3DX or DX+ for the time being, because no friends around me have such things. ...
If it is modified, play avatar mode. Every time the modified data column (DX+ is gold coin) is filled, the modified part will be given to you in the same order. You just have to choose whether to pretend or not.