[cybergas]

I guess I wasn't clear enough...
Yes, I know how to edit admin permissions, the second statement :

I've looked into administrator permissions: (username), there's not this option.

was referring exactly to where you point. There is no option "Can Administer Usergroups" on there for none of the admins.

This is copy and pasted directly from there:

Can Administer Settings
Yes No

Can Administer Styles
Yes No

Can Administer Languages
Yes No

Can Administer Forums
Yes No

Can Administer Threads
Yes No

Can Administer Calendars
Yes No

Can Administer Users
Yes No

Can Administer User Permissions
Yes No

Can Administer FAQs
Yes No

Can Administer Avatars / Icons / Smilies
Yes No

Can Administer BB Codes
Yes No

Can Administer CRON
Yes No

Can Run Maintenance Tools
Yes No

Can Administer Plugins
Yes No

Can Administer Notices
Yes No

Can Administer Moderator Log
Yes No

Control Panel Style Choice

Dismissed vBulletin News Item IDs

Right now I have the supermods with the 'Can Administer Users' set to YES everything else to NO.
This gives the supermods access to modify Usergroups; even their own to whatever they want, I have setup a supermod account which I'm testing this. The only way I could stop them to modify this is through marking them accounts via configh.php so they cannot modify it, but either I the main admin cannot modify it without going to the config.php first

With my tester supermod user I have change my user group to only admin and what happened is that the user is promoted to admin on the 'Forum leaders' page but still remains with the same access to ACP, no extra permissions or ACP access is granted.

Additionally we have a hidden forum that only 3 people can access (admins) this is to avoid tons of PMs and we can keep on same page, what happened when the supermod 'was able' to change his user group, then it automatically grants access to this hidden forum for supermods who should not be able to see to see this forum.

Anyway, I would like to have that option you mention 'Can administer Usergroups' it is simply that is not there?