Perhaps I misunderstand the question. but I thought you were proposing to ask Costco to void and resubmit the transaction at the same price. If this is accurate I don't understand how the price protection process would be relevant.
Your understanding of my question is perfect. My latest comment was relating to credit card adjustment possibilities without the product being shown to the cashier.
Nevertheless, I understand your comments to indicate that it will be not possible to have charges reversed and put on the other card.
On the other hand, I can bring the item to the store, I would rather not as it is a computer system and will be setup by that time (under 90 day return time). Other item is the medication that I need to fill before the new card shows up (strictly speaking it usually is not returnable, I know that).