This is of course with the assumption you are using Papiao services since other services aren't allowed to be discussed here.
I have tried this method and it simply does not work. I have an AVOV box and a Buzz box. Since I cannot change the AVOV mac I changed to the Buzz mac to match that of the AVOV box. This was in the hopes I could move from room to room with ease as long as one box or the other was turned off.
I turn on the AVOV box and it connects and I can watch TV. I turn off the AVOV box go into the other room and turn on the Buzz box and it simply will not connect. I go to the Papiao site and do an IPTV reset and now the Buzz box will connect. I turn off the Buzz box go back to the other room turn on the AVOV box and it will not connect. I do an IPTV reset and now the AVOV box will connect. It's an endless circle.
The point of entering a different MAC into the Buzz is to match another boxes MAC (even if it's another Buzz box) for ease of moving back and forth between boxes. I have found this is not possible without constant IPTV resets which defeats the purpose. If I have to IPTV reset every time I switch boxes I might as well leave the original Buzz MAC alone.