I'm updating my forums by adding a lot's of new prefixes and I think there is something you need to add to the prefixes groups.
When you click on a Prefixe, you are able to select the forum you want it to appears. I think we should be able to do the same for groups so that we don't have to do it 50 times or use your copy button. Copying prefixes options should be use to prefixes in a different group and only for them imo.
ps: I also would like you to have a look at my old post here, if you have time : http://xenforo.com/community/threads/acp-forum-list-with-dropdown.64380/. I wanted to make a little up but I have seen it was forbiden. My forum looks like that : http://puu.sh/623D3.png It's awful to make modifications :'(