AWESOME! Just what I was asking for a while back https://forums.factorio.com/viewtopic.php?f=6&t=106656
This really should be in the core game.
The area of destruction has already been covered by someone else's suggestion already.
Like I say in my suggestion, it would be great to not destroy buildings that won't be replaced. Like a full chest would be removed (a lot of items now running around in inventory) just to have the same chest put in its place (now empty).
I suggested two options, Shift click like it works now, just clear rocks/trees. Then Ctrl-Click which will clear Only what is needed to place the blueprint, buildings included (like your mod does now) hopefully not replacing what doesn't need like I mentioned before. But a third could be Ctrl-Shift-Click for the area of destruction. Assuming your blueprint is 32-32 in dimension, ctrl-shift-click would level that 32-32 space first and then place the blueprint.

Great mod! You'll probably make it into one of XTerminators mod highlights for this.