Exactly. Or just enable the guest account. That's what I always do.
Having said that, prior to my recent visit (failing mbp fan) my trips had always been for failing/failed discrete graphics (about 5 trips on 2 different generations of 17" mbp) so a reinstall is inevitable because making macOS work properly after a mainboard replacemnt is more work than reinstalling from scratch
- Boot into single user mode...
# mount -uw /
# rm /var/db/.AppleSetupDone
# reboot
Reboot the machine and it walks you through a re-run of setting up the OS X set up assistant, which allows creation of an admin account.