Hogwash, you absolutely can run CNG or propane in a diesel engine with a properly engineered system. I was doing it ten years ago. Dual fuel, diesel/CNG or propane systems are a viable reality that save money.
It sounds like you are talking about some kind of aftermarket bolt on hot rod kit.
Cannot, unless you have a way to lower the compression ratio. The flashpoint is the flash point. Put some gas in your diesel and see what happens.