Hi Holly,
We were on the 1/31 Western Magic and we were told a bit about tables/seatings by our servers and the head waiter. They do hold out a couple of tables in the Dining Rooms for just the reason you mentioned. They also like to know if you are going to be gone for any evening, like Palo or eating on shore. So between the two there are empty tables to be had. Just not a bunch.
Even though we had told our head waiter we would be dining in Palo one evening, he called to see if we were sending our kids alone. (Ha-Ha - they are 8 yr. old twin boys, I don't think so!) At first it sounded like they were being nice offering to host the kids without us, but really, they'd like to know if the table will be free to use for diners that are switching seatings that night. So, no, they don't have unlimited tables, and if the diners haven't informed them they'd be gone, they don't always know. But, I think if you have a night you are ready early, call or swing by and see. I would just let your head waiter know you aren't going to show in your regular seating asap. Then there comes the matter of tipping your replacement servers that evening and for sure you should still tip the servers in your regular rotation even though you didn't show....well, that's another thread.
Juli