@OP why not register the Username that you want if your problem is the limitation you can buy the
Copper membership to increase the limitation it is cheaper around 40k sats.
Perhaps this is probably the best idea OP can get. I thought of it too, instead of struggle too much for an account that you're probably going forgo some day and just focus on creating a new one and surely @OP can afford copper member for lifting the limitations.
OP consider BitMaxz suggestion it's probably the best knowledge or idea you can get towards your want or least keep waiting for admins responses which is under probability if they would accept the proposal even if they get to see it.
That's another option to do if name change request has been denied. But he could still able to try to contact the administrator towards this request.
He cannot expect any fast response from them since provably it will take time for this request to get approve. But let see if OP could able to make this things happen since if he can change his name successfully then provably lots of people which have an issue might change their name. I believe its rare case that administrators allow this changes.
Although they grant certain individuals to change their names, but those guys are contributors of this forum and provably they look at the contribution done by those people.