So is it safe to re name the superadmin group owner?
Stuff will break, your server may melt, earthquakes, volcanoes would erupt.
Seriously though, no. Don't do it.
Gmod expects superadmin to be highest group.
Read the article. Superadmins have pretty much full access to do anything to your server that they want.
Don't give people superadmin unless you trust them with the life of your server.