If I buy 7 day tickets from ticketmania, and decide later to upgrade to 10 day non-expiring tickets, how will they calculate the price difference? Will it be calculated based on what I paid for the tickets originally from the discounted seller, or will it be just the difference between what WDW charges for the ticket I have and their cost for the new ticket? I don't want to end up losing the benefit of buying from the discount seller ( if ultimately I end up paying what I would have paid Disney anyway).