not one person I know who cares about some
thing as much as OP seemingly does, would ever book without looking at the equipment plus the seat map is kind of a give away for someone who seemingly knows so much, if you are flying first, I can’t keep track, who cares, anything less I don’t much like the seating, and yes the A380 can be an issue, there aren’t that many of them and they are bigger than the 777 so mechanicals make it harder to rebook

as to what you can rebook you can only book what is available and since you don’t seem to have status you might be a little farther down the priority list so all the good flights might go to passengers with status