This sort of thing happens all the time and, unfortunately, we are at the mercy of the carrier.

We had a situation a while back on a vacation flight traveling with our two (then) young children where CO made an equipment change and completely messed up the seat assignments. We originally had 3 seats on 1 side of the aisle and the aisle seat across, in the front of coach and ended up with 3 different middle seats and a window several rows away from any of the other seats. I called the Elite line and begged someone to put us at least 2 and 2 since my kids were too young to fly without sitting next to a parent, not to mention the whole middle seat thing! I was told that it would have to be dealt with at the airpport. If anyone on this board has ever flown the EWR-PBI route, you will understand how impossible a task it is of asking people to change seats (especially offering a middle seat). It was a disaster and I recall at the time calling Customer Care and writing a letter to complain about the unfairness of the airline being able to just change around the seats so randomly with no regard to what the customer "bargained for".

So while I sympathize with the OP, I just don't think they have a policy or procedure that effectively deals with the predictable result of changing flight times, equipment, etc. because let's face it, a number of people are inevitably inconvenienced but they have reasons for making the changes that from their corporate viewpoint outweigh the inconvenience to their customers.