@ onkelf - good for you - go for it.
My advice would be to grab yourself an assembler though.
You'll be able to find Devpac, AsmOne, AsmPro, PhxAss or Macro68k all over the place on the internet.
If you have trouble finding these, come back to me - I can supply you with any or all in .adf format or, if you really need real disks I can write the .adf's to floppies for you and send them - just PM your address if needed.
In my opinion you don't want to be poking assembly mnemonics into memory with Action Replay really - you'll get frustrated and annoyed at not having a proper assembler pretty quickly I'd say...