@ OGT -- Sorry, I missed your post. Let me look at that.
@BLackxRam - This is what this hack does. It adds a radio button into the modify Usergroup section of the Admin CP that says "Modifiable Group" Y/N. If you have this radio button set to Yes on the usergroup, it will show up in the dropdown for the mods. If you set it to no, it won't, so they can't change people into it.
Edit to add -- OGT, that one is a typo that was entered twice but won't hurt anything. I didn't include Banning as that is a seperate permission and I didn't want to exclude those who can't ban from being able to change usergroups. You can take that out as a duplicate entry, or if you want only those who can ban to change groups, change it to canbanusers.