If you are testing xml files, I found using SERVA and a VM in combination sped up the unattend.xml testing process exponentially. FOG is a far more capable production imaging server, but SERVA lets you implant unattend.xml files into your .WIM files on the fly, so you can essentially make an edit to your .xml, reboot your VM, set it imaging. Once that’s all tidied up you can do the proper adjustments to make it work as a FOG usable golden image.
The licencing thing… I spent a year tooling around with that stuff, can’t say I got anywhere. It would be interesting to google for: “OEM activation” or look up stuff about SLC. Perhaps have a look around on an old Dell win7 recovery media cd for stuff, I always like to look through human readable scripts, maybe you might find something useful. Perhaps you could put together what you found as a post installation task. Sure would be nice to have all those OEM keys, per machine, re-register after a golden image is dropped.
Seriously though, for testing unattend.xml, figure out how to use SERVA. It is an elegant little piece of software.