@Rebbetzin
I both a seat in a specific location. Let’s call it row B seat 6 (a made up location). If the shul expands and adds additional seating, but my physical seat is still where it was, then that is my seat.
If the shul wanted to remodel and move seats and rows (adding 10 feet might change where the bimah would be located to keep it central) then the shul would have to negotiate with owners of life interest in specific seats. The shul could not just move a purchased seat.
I don’t see such a thing happening, as I’ve said before most suburban shuls were built for the baby boom of the 50s and 60s and have far more seats than needed today.