Yeah, I'd imagine your reasons would have satisfy Theymos and not be trivial.  Coolcryptovator recently got his name changed to all-caps because he had some sort of telegram impersonator, whereas I couldn't get my username changed because, well, I had no reason other than I just wanted it changed.  I'd imagine that Theymos gets lots of requests for name changes and if he started granting them to everyone who asked, it'd turn into a full-time job.

Besides, as mentioned it used to be something that was reserved for donators.  It would suck for prior donators to the forum if suddenly Theymos started granting name changes to anyone who asked (even though 50BTC was worth a hell of a lot less back then, it was still money out of one's pocket).

So the bottom line is, OP, if you're even thinking about asking Theymos to let you change your username as a Newbie, forget about it.  If it's something you really want to do, just create another account and start fresh.