Well, after going through the GUI to attempt doing this and failing a multitude of times with "User does not exisit!" (well, no kidding) I finally tried to just add a new user so I could get rid of the default 'ubnt' account from my EdgeSwitch by following the CLI primer at https://community.ubnt.com/t5/EdgeMAX/EdgeOS-CLI-Primer-part-1/td-p/285388 only to find that the commands aren't actually valid according to the EdgeSwitch.
I'm working with an ES-24-Lite on firmware v.1.7.0.
So, now I can't believe I am going to have to ask this but how do I actually add a new user with Privelege-15?