It's nice that you would allow someone to take your first class seat and as long as it is arranged prior to getting on the plane then there is no problem. There should be no swapping at all once the flight is underway. For any reason really. It's not fair for those that have paid to be up there to see people swapping seats. Whether its for the better meal or a better seat to sleep in. Too bad - you decide who sits up there before you get on and then that's that. That's like going to a buffet and once you've eaten then letting someone else come in and take your place. It doesn't work like that. Some flight attendants may look the other way but I have more respect for those seated up front then to let one person take away from what the others paid for or are using their hard earned miles to pay for.