Maybe I'm missing something in this thread... If you already have an AP and have a picture on file with Disney or have had an AP in the last 12 months, then you do not need to go to the AP processing center to make changes to your AP. We have bought new APs right at the ticket windows and had them printed there since we had pictures on file from the last time we had APs. If you want to upgrade your pass on a blockout day, you should not need to buy a blockout ticket. You should just be able to take your AP to the ticket window, pay the price difference between the AP you have and the one you want, and they will print the new AP right there at the window for you. If you only have an AP voucher and have never had your picture taken, then you would need to go to the AP processing center in either park.
BTW, I've read that there are some changes happening to the APs starting today, but I don't think they are relevant to this particular question since we seem to be discussing an already active AP.