Occationally someone posts that they didn't have luck changing, so the best idea is to hope for the best and plan for the worst. There are some advantages to late seating. A lot of people feed their kids earlier from Pluto's or room service or something, then either have the kids in the club, let little ones nap in a stroller, or let them snack at dinnertime.
I have heard, I don't know how accurate this is, that when main seating gets to a certain capacity (but not yet full) they start putting people on the waitlist and booking late. This lets them have some room for people with medical reasons for early dining or other reasons to move early (someone posted linking your reservations with an early dining Diser will work). When they have a better idea of who is sailing, they start moving folks off the wait list.
Good luck. Most people are either switched ahead of time or switch at boarding.
(But I think the chances of a party of 19 being able to switch are very slim).