You can put an update capsule in that region and it will be picked on reboot. Another option is putting a file in ESP then telling EFI with a special call that

You can put an update capsule in that region and it will be picked on reboot. Another option is putting a file in ESP then telling EFI with a special call that there's an update to be applied (special call is also needed to inform EFI about the memory update method). Windows Update uses those to deliver firmware updates on behalf of vendors.