If I purchase say a 4 day hopping ticket from Undercover Tourist today and then when we go decide we actually want 6 days. Once I go through the gate, can I then upgrade and pay the difference in gate price from the 4 day to the 6 day?
If you go to the locked sticky Everything About WDW Tickets in the TPA&S Forum, especially Post #6, you can get a lot more information. An easy way to get to the sticky is by clicking on the link in my signature.