For some reason my miner got a new IP from the router even though I set the same mac-address as with Bitmain FW. However we put BOS into my friends miner simultaneously (connected to same router) using his Bitmain FW-mac and got no conflicts. I can't remember if his miner got a new IP though.
Just saying that don't be to sure about the "it would have the same IP address as it had with the factory firmware" part.
BR.
Steff