We were able upgrade our SCCP from a 3 day hopper to a 4 day. It costed us $15.00 per ticket to do so. We did this at the ticket booth. Just beware that you might get inconsistent replies from different cast members like we did. First I went to Guest Relations to ask how much it would cost us to upgrade and was told "since these are discounted tickets, unfortunately they are not upgradeable". I knew otherwise from previously reading the DISboards (thanks DIS ) so I tried again to ask the same question at the ticket booth the next morning. The cast member was very helpful - he took a while to research in the computer how much it would be, but finally got it done. He gave me back my 3 day hoppers and said that I could use those, but then called me back to the booth saying that the computer printed new 4 day hoppers. They will manually write down or date stamp on the new 4 day hoppers the days that you have already entered the park. My sister tried to upgrade hers later in the day and was told that it would cost $150.00 to upgrade the 3 tickets in her party! My sister went back later in the evening to another ticket booth; the cast member had to ask her supervisor how to do it but was able to do it pretty quickly and it costed $15.00 each. So just be aware that you might have to be persistent!
We have done this multiple times. The cast members are so well informed and helpful. They take the time to tell us what they all they were doing and got us on our way quickly. I don't remember how much it cost us, but for a family of six, it was a do-able ammount. Have a great time~