Surely, SRB2WikiSonicMaster, with your experience in all three of those areas: Sonic Vegemite, VGMusic, and the SRB2Wiki, you could've just used either of those and merged them with your nickname, SonicMaster. Honestly, I like Begin's nickname for you (WikiSonic). It shows your accomplishments on the SRB2Wiki, and it also shows that you are connected with Sonic in some way, shape, or form. Though, it might be too late now, but still, it would've been a better choice (on this whole nickname conflict, considering "SonicMaster" is very generic and uncreative).
I'm sure if you bug an Administrator enough times, you could get it changed, but seriously, SRB2WikiSonicMaster is not only long, but just generally annoying in my opinion. =|
</rant>