I needed to move to a new USB, but wanted to 'start from stratch' while keeping my current Unraid Basic plan.
From my Old USB Boot drive, I copied /boot/config/Basic.key to my new system under the same path and name. This required manually mounting the the old boot drive to my new system and later unmounting. I also had to move the Trial.key (to Trial.key.backup) so that Unraid wouldn't be able to find that.
On reboot, Unraid recognized the incorrect key/guid and offered me the annual option to replace my key.