As a follow up to this.
Our SE got back to us with the explanation that in our case we wouldn't need to do a clean install via USB. While this is true, it would have made things much easier and quicker as there are 2-3 steps to get where we wanted (r81.10 JHF).
It seemed otherwise like we would have to contact TAC, first to actually get in to BIOS or BIOS Boot order. This would have been done with a BIOS password and TAC would have to reset the password afterwards.
It would have been great to allow a Boot order with USB first and then HDD like for gateways, if for some reason we can't get into GAiA anymore.