Out of curiosity, why do you need to restrict use of custom commands? Does matter if the user types "/slap Username" or "/me slaps Username with a wet fish"?
The user can do nothing with custom commands that they cannot do with text.
Out of 87 pages on the vB4 version alone we have not had a single request up until now to disable custom commands for certain usergroups - that I can remember, anyway
Fillip