Heres what I'm thinking...
First, Nikkol is right (Shes always right ) because on almost every page you see stuff like:
if mlev = 4 then
.....
end if
you would have to change that to mlev = 5 and then DB changes as well... IMO not worth it.
BUT you could look at Nikkol's Usergroup Lite MOD and see how it works. It shouldn't be all that difficult to do what you want.