can you book a main cabin ticket on american an then upgrade to main plus afterwards and if so would that credit apply? I think if you book main plus at the time of booking its all coded together in 1 transaction. Asking because on a round trip flight with 4 stops (2 there and the 2 back), main plus is only $94 per person and gets you access to choose all 4 seats in main cabin extra, instead of having to pay for 4 main cabin extra seats separately although I know that would trigger the amex credit