I'm a Marco Polo Gold but only a QFF Bronze. When I booked a Qantas international flight recently, I put my Marco Polo number on the booking because, as a Oneworld Sapphire, it allowed me to select seats for free. But travelling on a cheap sale fare, I wouldn't get any Marco Polo status credits or miles for the ticket. Can I just ask to substitute in my QFF number onto the booking when I check in?

The only downside to this that I can see is that once I am a lowly QFF Bronze in the system, there's no chance of an op-up. But what are the chances of an op-up for a Oneworld Sapphire on Qantas anyway? I assume Qantas gives priority to QFF Platinums and Golds (and possibly Silvers) before Oneworld Sapphires? (Not complaining, CX does this in reverse...)