Yes, you can add multiple cards to your Skip account. When adding more cards to your account you must indicate which card you would like to set as your default card. This option can be chosen via the payment screen once you have added another card or toggled to your card of choice in the cart before checkout.
From here you can tap on your desired card and make it your default card as well as change that card's nickname.
Please note that changing your card to default will move all future purchases to this new default card.
You can select a new payment option at each order by toggling the payment card option in the cart before checkout.