Originally Posted by eponymous_coward

You bought the ticket from AS, so if you want to change the ticket, you deal with AS's rules on that. VX is the one you have to deal with when it comes to same day change because on the day of the flight, they are the ones who will deal with the ticket because they are the ones flying the plane, and they will control the ticket at that point. (They are still two separate airlines as far as that goes).

This is a really common problem on FT we've seen: people assuming "oh, Airline X bought Airline Y yesterday, so it's really the same airline and I should get to pick and choose how things work". Well, no, it's not and no you don't. It's a good reason to avoid doing a "I buy a ticket on Airline X from Airline Y" scenario to avoid these sorts of situations.