Fantastic mod, no idea why this isn't base game.
I don't suupose there is anyway to add some kind of filter such that you can only replace certain tiles or even the absence of tiles? I know a lot of people are using the mod to paint fill large areas ahead of layering more complicated blueprints and being able to control what gets painted over would be amazing,

Sorry didn't see your comment! More likely to see Github issues.

I like where you're going - could you give me some concrete examples of the type of things you're trying to do? Feels like getting the UI right might be difficult, but definitely open to feature in this area.

I also didn't see the reply so fret not!
I was thinking something similar to the current upgrade planner, given that different concrete types can be effective straight upgrades for movement speed I always thought it odd this never worked.
Give the tool one slot to specify the tile to be placed and a check box to ask if you want to overwrite exisiting tiles or not. Then a filter that takes a second tile as the one to be replaced.
e.g
I want to fill this city block with stone brick but not overwrite my pixel art in the middle, so I check off "Overwrite tiles" and select the whole area
Or
I want to upgrade the hazard conrete with refined hazard, so I add hazard concrete as my filter and select the area