First of all, this was actually originally found
HERE by n9ne
However the code was erroring, and it also had excess code in it and proved to be insufficient.
I took the code and fiddled around with it, because i had been looking for something similar and didnt feel like writing my own hack, however i ended up doing it anyway ~_~ and also rewrote the instructions.
Now anyway, this will replace the [ban] link in the MOD control panel, with [unban] for users which are banned when searching for them. Then it unbans (i bet you werent expecting that), similarly to the way in which you ban users in the first place. The instructions include information for things like changing the usergroupid which the banned users are in, and also for multiple banned groups, and for changing the usergroup the unbanned users go into. changing things is simple enough however if you need specific coding done just post it and ill post back the fix.
Works for ALL 2.x.x boards, 4 edits to mod/user.php
have fun...