https://www.youtube.com/watch?v=A6UcHYZt9l0This guy shows how to make a nes game genie code, by ram searching, debugging, and then experimenting.
From what I can tell, he was doing a great job showcasing how to make an actual gamegenie code.
Is there more videos just like this? Not those dumb/easy infinite life codes, but actual codes where you have to debug constantly.