Is it possible to replace the throttle body on a fuel injected engine and run it on propane?

Is it possible? In theory yes it is but a simple propane carb or mixer would not work. You would need an aftermarket box that would intercept the ECU's pulses to the gasoline fuel injectors (to shut them off) and convert them to control the propane flow rate instead so that the stock ECU would still be in control of the mixture. There are also special injectors that replace the gasoline ones and inject liquid propane instead but liquid injection is more complicated than vapor injection because without a booster pump to raise the pressure as soon as the fuel rail temperature gets a single degree hotter than the tank temperature the propane starts to boil and form vapor pockets in the rail and fuel lines which vapor locks the system and kills the engine. I don't know where to get the kits however and one probably doesn't exist for your car anyway. One problem with with Propane is that if you don't up the compression ratio of the engine to 12 or 13 to 1 you will see a performance and mileage loss as propane has a higher equivalent octane rating than gasoline but it also has less BTUs per gallon.

just like making it work on LPG/CNG there is a mixer unit that bolts onto the throttle body but you might need to modify bits to make it work, as long as you have the will power and know what your doing its not impossible!

i've even worked on some cars where the LPG/CNG mixer is directly bolted ontop of the carburator.

yes