Someone else was doing that same thing not too long ago. They were using a plugin on hook fetch_musername to override the markup.
Edit: here's one of the threads:
www.vbulletin.org/forum/showthread.php?t=285209. It's for vb3 but I think it's the same for vb4. It's a little complicated because he was trying to cache the markups, but you don't really need to do that.