If you want try use other rom, you need change the rom of the exe by other using an hex editor such us HexEdit avaible on http://members.tripod.com/AndrewPhillips .
    The Rom must be a MSX1 16Kb Rom with NORMAL 16/32KB START ON &H4000 mapper.
    When you edit the exe´s you´ll find the rom at these positions:
 
 

You can also search for ABO@ (the first four bytes of Road Fighter roms), and substitute the next 16Kb.
I only had succes with R.F, and A.A. , so if you achieve something send me an e-mail.

   Sd-Snatcher strikes back again with a little program that patch the Psx msx executable file in order to use your our roms. You only have to rename any exe of the msx.zip file by fmsx.exe and put the rom you want in the same directory of the program and fmsx.exe.