I'm aware you dont intend to add an option to disable it directly, but i would like to know what in the files i'd have to edit to be able to turn it off, as I enjoy the increased difficulty with biters but would like my mostly water save to remain mostly water, instead of slowly being landfilled in

I was against the abolition of landfill even before Factorio 2.0, but with the release of the DLC, players have the ability to remove landfill with drones, so this is even less relevant.
The player must at least occasionally pay attention to what is happening on the perimeter.
It is also a very important part of optimization to prevent lags. Too narrow passages that cause lags naturally widen over time.