Interesting extension. I did some testing and found some issues (well, maybe they are not issues, but features):
1. If you planing to add admin settings, it would be nice to have there note saying if username changes is allowed on forum or not (on my test forum it wasn't allowed, but I didn't remembered it, so it took me while to figure it out).
2. I did have problem with changing my username in UCP, because phpBB wrote me, that I have to change password too (maybe this is bug in phpBB), so I made a few unsuccessful attempt to rename myself - it seems that those attempts were recorded and listed by extension, even if my username wasn't changed.
3. There is not listed last username change into actual username. I know, that this extension shows previous usernames, but for me it would be nicer if it shows last username changes.
4. I know I can change it in language file myself, but I think it would be clearer if
Changed via: Profile
would change to something like
Changed via: User's profile