Last night, I submitted and paid for 4 comics to send for the Jeremy Renner signing. As fate would have it, I ended up finding a West Coast Avengers #1 this morning that I want to add to the pile. Am I too late to open up that order and add that book or do I have to submit it as an entirely new order, which would include a separate shipment?
I'll answer my own question, in case anyone else asks the same thing.
The CGC does not charge you until they receive shipment, so all I had to do was start a new order, include the extra book, print the new packing slip and inserts and send that in. Problem solved!