I have a flexible spending account through work that I'd like to use for an upcoming trip on Amtrak. I have enough in my account for the base rail fare, but I'd like to get an upgrade, which I'd have to pay for separately.

So...

(1) Can I use both the flexible spending account Visa and another credit card to buy a ticket-using 2 credit cards as payment when I initially buy the ticket? Can I do so online?

(2) Can I buy a regular ticket now and upgrade it later? If I do both parts of the transaction within a few days, the base railfare shouldn't have changed much, so would the card I use for the regular ticket (my flexible spending account Visa) be re-run as part of the upgrade?

Thanks.