I don't like the idea of using oil or WD40 to kill primers in cases because then you have to wash the cases with detergent and hope you got all the oil out of them. I've never tried to deprime crimped primers with a size/decap die in a press, but I've deprimed a lot of commercial cases without incident by going slow. Run the decap rod down far enough that you're feeling only the resistance of the primer, and not partially sizing the case. You'll be able to feel the primer slowly backing out.