Nick

Thanks everyone for the replies. I missed out on the last sale they had not too long ago because I only added the package to the cart and didn't actually purchase it. Unfortunately no on board credit for our upcoming cruise but thankfully I saved a little by reordering the package with the new sale. Thanks again for the help everyone! 

When you cancel a CP purchase, they completely cancel that transaction and refund the card originally used to make that purchase. I usually see the credit refund on my card in 3-4 business days. When you then re-purchase the item, it's a completely new transaction. Sometimes the credit refund hits your credit card on the same day as the new purchase!
Unfortunately, they do not make adjustments and credit you back the difference with Cruise Planner purchases. Even when I called customer service one time to cancel and re-book a cabana, they had to cancel the first transaction and then create a new purchase.

@Nick, just to add to this, if you made the original purchase using on board credit, that OBC will appear back in your account immediately upon cancellation and available to use for your new purchase.