Just to say *many thanks* that the above worked great. If anybody needs to restore their data (serial, UUID, etc) onto fresh BIOS those definitely work (EVGA, ASUS). The integrated Ethernet MAC seems to be part of the Gbe firmware that is part of ME on Intel and I just transferred that blob onto the fresh BIOS and that worked great also.
I'm in the same boat with my X299 Micro - I have not been able to mod it either unlike Asus/AsRock/etc. - thus I've had to ask pretty much each update. The Micro does not have BIOS switches but I have been able to buy compatible chips (Winbond not original Gigadevice) to swap when testing mods...