I edited the  libvirt xml (virsh edit...) file of a running Windows server instance because I changed the video model type from cirrus to vmvga so it can support a higher resolution on a console (cirrus supports up to 1280 only).

After editing, i "soft-rebooted" the instance and the new configuration sticks.  That's awesome.

But when you do a "hard-reboot" it will revert back to the original config.

I also tried to do a "shut-down" then "start" again, but it still reads the original config.  Not sure where it  is reading the config from...