I know I've been wondering that as well. I'm upgrading a ticket one day to a power pass and my first day might hit the end of the blackout period.
On a related question. Am I correct in assuming that I need to upgrade my one day ticket to a power pass at the very end of the day because once I upgrade I won't be able to reenter the park? I'm planning on going January 2nd or 3rd, which ever day I end up flying into Orlando, to see the Christmas decorations before traveling to Disney. The rest of the Universal time will be the end of the next week and well past the blackout date.
To the OP, if you're planning on buying a power pass, you may be able to use the same "trick" buying 4 day ticket then upgrading it to the power pass before the last day expires.