Please add a confirmation for "Select New Contents For This Blueprint"

[sarge945]

Currently, when using the "Select New Contents For This Blueprint" button, the blueprint is saved immediately upon selecting a new area. This is potentially VERY destructive if we misclick or select the wrong thing. There's no undo and no way to save your blueprint if you make a mistake, from what I can see.

Replacing the blueprints contents should be undoable by discarding changes, similarly to most other blueprint changes.