If you are like me and you don't want to use third party admin mode and you make your own tools than this can be very useful for you. This basic plugin will handle usergroups on your server for SteamIDs of your choice. On 'sh_plugin.lua' on the 'PLUGIN.Users' add the IDs you want and whatever usergroup you want them to have.
And lastly: There's no need to use the 'user' usergroup since this one is set by default.