I was trying to create a new user and a new group with the IDs of 1000 (requirement) but I ended up not being able to log in to the account in a regular way from the Login screen, however login from the terminal worked just fine. All I got on the Login screen was an endless spinning wheel and the user didn't show up with the other users. Any ideas?
I created a new group & user from Users&Groups in Preferences and then changed the User's GroupID to 1000 manually in the advanced settings. Trying with
dscl in terminal yielded no better results.