It was too tempting not to test, so I went and tested the other half.
On an 8.3 host I set the preferred resolution to 800x600 in the OVMF menu on a UEFI Debian VM, turned that VM into a template, and cloned it.
The clone came up at 800x600.
A control clone of the same original, with nothing set, came up at 1024x768.
So your workaround holds, the resolution really does ride along into VMs built from the template.
For anyone who wants to poke at it, the setting is a UEFI variable called PlatformConfig under GUID 7235c51c-0c80-4cab-87ac-3b084a6304b1. It only appears in NVRAM once you commit it in the menu, and it stores width and height as plain little-endian integers, which is why it travels with the VM record.
One thing I didn't expect: the OVMF help text says the mode list is filtered against video RAM size, but the VM I used had the default 4 MB and still offered everything up to 1280x1024.
So you may not need to raise videoram for the common ones.
Fair warning though, I measured the console at the firmware stage rather than after the distro's own driver takes over, so a guest that sets its own mode later could still override it.
At least, that's my understanding.
