I would be VERY careful. In fact I would not try it.
Diesel is a flamable fluid, it does not explode in the cylinder. Pressure from the piston driving up in the cylinder creates heat, as the diesel fuel is injected into the cylinder, it burns and causes expansion which drives the piston down.
Gasoline and Propane, when used inside internal combustion engines are exploded by a spark plug, the resulting explosion drives the piston down.
Propane in a diesel engine will have no ignitor other than the pressure which generates heat, it is going to be timed completely differently and it is likely that the timing issues alone will create a situation where IF the propane ignites it will very likely create a small explosion at the WRONG time and I have no clue if the consequences would be good or bad, but I suspect it simply either won't work or it will be dangerous.
I know of know multi-fuel engine that would allow diesel & propane to be substituted for each other.