TL;DR
A blueprint should be able to include deconstruct entities.What ?
When editing a blueprint one can remove entities, which makes the disappear from the blueprint.One should also be able to mark tiles for deconstruction. Then when placed and any entity is at the location of the tile is then marked for deconstruction.
Why ?
Blueprints are there to be used, to place many copies of the same thing on the map. But what if you later need to change things?For example I have a blueprints for the train networks with stations, junctions, long straight parts with all the right signals included. I started with LC trains but later I switched to LCCL. For that I have to remove half the signals on all straight parts. It would be great if I could mark the signals for deconstruction in the long straight rails blueprint and then place that on top of all the straight parts.
Or I have a blueprint for oil processing. Later I notice the pipe throughput is insufficient and want to add a pump. I can update the blueprint but then I have to manually remove the old pipes by hand before placing the blueprint over the old setup. Would be easier if I could make the tiles below the pump for deconstruction and then the blueprint could be placed over existing setups directly.