"For anyone needing this process for themselves after testing this morning following u/jay0lee advice, this is what I'm planning on doing
Move Senior Grad devices via serial number csv to OU with the Chrome device setting force re-enrollment turned off.
Command to move devices into desired OU: gam csv "FILEPATH" gam update cros query "id:~~serial~~" ou "NEW-OU"
Command to powerwash devices that are in the "NEW-OU": gam issuecommand cros "query:orgunitpath:/NEW-OU" command remote_powerwash doit
The powerwash command will be pending on the device until the next ping and then it will wipe itself.
After that, the only thing left to do is deprovision from your fleet in the console using the original command in this post: gam csv "FILEPATH" gam update cros query:id:~~serial~~ action deprovision_retiring_device acknowledge_device_touch_requirement"