this has been my experience when upgrading, this has happened to me twice, once with our first AP's in 2007, again with our last AP's in April 2011......
We had purchased park hoppers, we upgraded our last day of use which was a blackout day. We did NOT need a blockout ticket, our brand new AP's worked just fine for admission, hopping AND fastpass gathering. We did not need to mention we were upgrading on a blackout day, we simply went to the ticket booth or the AP processing center (which no longer exists) and upgraded, paid the difference, did the photo, left with our new AP's. Unless they've changed something since last April you will not need a blackout exception ticket.