Say I have elite status on one airline in an alliance but I want to accumulate miles in another airline in the alliance. Can I give one number for the purpose of status recognition and the other for earnings, on the same flight?
I thought I remembered this was possible, but I forget the details. If so, what should I tell the travel agent in order to do this?
It is possible (for an unusually knowledgeable travel agent), but not easy.
There are two fields in the PNR for each airline, the FQTV field (frequent traveller number for mileage earning) and the FQTS field (frequent traveller number for status purposes).
These can be set to different values. But airline IT systems are not always designed to understand that this can happen, so even if you manage to find a travel agent who understands what you are talking about, it is not guaranteed to work.
If you use a tool like the free MyFlights tool, it will tell you which numbers you have attached to the booking and whether they are FQTV or FQTS (or another type of FQT number). MyFlights is only available for Amadeus bookings.
So I am no expert in this but the method described in all the fancy travel blogs I follow, in the case the strategy described by @Calchas above (+1) fails, is to try to enter the lounge with your status card. If the lounge agent insists that the status program must also be the one that you earn miles for, have them change it on the spot, get in, and change it back to your preferred earning program online as soon as you are inside the lounge or at the boarding gate. That assumes you know how to do so (and it being possible).
Also be aware that sometimes it works and sometimes it does not (link credit @Berwyn). YMMV
