That's what I wanted to suggest to you.
I did the same with R4_1.18 + cheat code patched (1.18 has a problem) converted to M3DSS
I see you found yourself how to do it
you need to patch a file to enable the cheat code again. there's a .exe to run.
it's on the download section if you need, or I can have a look if you want.
I see YSmenu is suggested for M3DSS too, I have a question regarding this firmware :
I now people still using it, and I know they will want to play newer games.
Does YSMenu works with M3DSS originally, or is it for R4 and I need to use the converter tool to change it to M3simply ?