Deploy a computer-level configuration profile with a Wi-Fi payload. Test first and don’t delete the payload without adjusting scope to None first, as always.
Tried this, pushed a computer level configuration profile with a Wi-Fi payload. Removing it is prevented UNLESS the user is connected to it, then they can click "Forget this Network" and have it removed.
I don't think there's a way to do that. Even using the
/System/Library/PrivateFrameworks/Apple80211.framework/Versions/Current/Resources/airport prefs commands I don't think that button can be locked down. And even if you could, those prefs are only to prevent non-admins from adjusting any of the settings in Wi-Fi, and since you mentioned these are admin level users... honestly you're really looking at removing admin rights from users to prevent this. I know that's much easier said than done, but I suspect there won't be any other way.