umm i use different toe/heel pieces but of the same brand. not sure if that helps for. for instance my urban skis currently have a px12 toe and p10 pivot heel on one of the skis.
its not a good idea, they are designed to work together. The only way I would think of someone doing it is if the are from the same line but maybe a different din, but even then im not sure why they would do it.
My friend breaks his p12 heel piece, thats it. He mounts a p10 heel piece in his place. Skied that fro about a season and it did him okay. Only thing is that he was riding his din at 10. which wasn't too grand on the bindings.