Can’t Delete Original Admin User on macOS High Sierra

I recently migrated to a new MacBook Pro. The old one was on High Sierra, but the new one wasn’t. So I created a temp “admin” account to do the upgrade, then do the migration with Migration Assistant.

All seemed okay, but when I went to delete the original user account, I couldn’t. And I don’t mean “you don’t know how to delete accounts” couldn’t. I mean, I tried every possible way, and it wouldn’t couldn’t.

I found this thread on the Apple forums with people having the same problem. After trying everything else, this is the solution shared in one of the replies that worked. Warning, I have no idea of the side effects this might have, but so far so good for me. Also, do not come crying to me if it totally hoses your machine. You’ve been warned!

1. System Preferences > Login Options > Join… > Open Directory Utility…
2. Click to unlock it. (You may need to Enable Root User in Edit menu.)
3. Go to Directory Editor. Search to find the user you can’t delete — the original user that was logged in when upgrading to High Sierra.
4. Find the GeneratedUID field on the right and copy it somewhere safe.
5. Change one digit in it and Save.
6. Find your new/main user account > GeneratedUID, paste in the one copied above. Save.
7. Run `diskutil apfs updatePreboot disk1s1` in Terminal.
8. Reboot.