If I understand correctly, you created a sys-usb VM (which hid the keyboard from connecting directly with dom0) and you enabled sys-usb to pass the keyboard through to dom0.
If so, then allow the keyboard to connect directly with dom0 so you can shutdown sys-usb and reassign the template.
In dom0 type:
sudo nano /etc/default/grub
GRUB_CMDLINE_LINUX= and remove
Save and close.
grub2-mkconfig -o /boot/grub2/grub.cfg
Reboot the system.
After rebooting, shutdown sys-usb, change templates & restart sys-usb.
Then go back to dom0 and replace
If you are “paranoid” disable local networking, before, during and after the system reboot while dom0 is exposed to the keyboard.
[disclaimer: take my advice at your own risk. If you are feeling cautious, wait until my advice is corroborated by another forum member. If you’re feeling adventurous… go for it! It’s just a bunch of silicon and electrons!]