[Xenon]

the first thing is easy:
find

PHP Code:

      if($lastpost[userid]!=$bbuserinfo[userid] || (time()-$lastpost[dateline])>3600 || ($attachmentid and !$foruminfo[moderateattach])) { 


and just add the usergroupconditions:

PHP Code:

      if($bbuserinfo['usergroupid'] ==6 || $bbuserinfo['usergroupid'] ==7 || $bbuserinfo['usergroupid'] ==5 ||$lastpost[userid]!=$bbuserinfo[userid] || (time()-$lastpost[dateline])>3600 || ($attachmentid and !$foruminfo[moderateattach])) { 


a toggle would also be possible (with a bit more work), but i don't see the effect there?
i mean if they want to add it to the last post mods should be able to edit