One of my friends was going to do this recently on his trip in December and they wouldn't let him. He had previously had an AP but decided against renewing when prices went up this summer, and then decided he would upgrade his tickets on this trip because he missed having it. He called up in October and the CM he spoke to told him he must have a valid AP or AP voucher in order to book the rate. He called back several more times and was never able to get it, so other peoples mileage may vary with this, but I know recently it appears they aren't allowing it. I see it as another little loophole Disney is trying to close if they have changed it, I could definitely see that being an issue.