Originally Posted by
Goldorak
It will work but the agent at the lounge will likely change the FFP number in your booking and so you may end up with your miles credited to SM instead of FB and it will be impossible to make the transfer (both airlines will refuse to do so). So, make your choice for what you value the most.
That is a risk, even if I have never seen agents doing that (I have done the same for a couple of months when I repatriated back to France and I have never had that issue).