Manually edit full name mac users & groups [duplicate]

Solution 1:

If you want create a new Administrator on your Mac, you need boot in Recovery Mode. (cmd+r at boot) . If Filevault is activated, from Disk Utility, you unlock/mount the System Volume giving the password. (right click on the system volume). You quit disk utility, then on top menu you select Utilities/Terminal I suppose the System Volume name is "Macintosh HD", the command is :

rm /Volumes/"Macintosh HD"/var/db/.AppleSetupDone

If no error message you reboot the Mac and then you will be invited to create a new administrator.

Then you can modify and repair your initial User admin account.