We didn't try your exact approach but we had issues trying to use snack credits for additional cupcakes. When we got to the cash register they told us they could not do that on pre-orders. It was what they called a 'split' ticket, which they could not do. We had to pay out of pocket for the cupcakes and ended up not having time to use those snack credits elsewhere because it was our last day and it took them a very long time to get us our food (don't know if that was related to whatever they did at the register to allow us to pay cash for the cupcakes or not). It probably doesn't matter too much how you order it because they're going to have to make the changes at the register anyway. Good luck. I'd be interested in hearing if it works for you.