Right now, i'm using the assembler WLA-DX to inject the SimCity base ROM with code changes, and using the SNES emulator Mesen with it's wonderful debugging tools to figure out what the hell i'm doing. I have a keyboard shortcut in Notepad++ that activates a .bat file, injects the base ROM, checks if it built properly, uses a powershell script (written by ChatGPT!) to convert WLA-DX generated labels (.sym) to Mesen debugger (.mlb) format, and if all is well, it starts the emulator with the built ROM and label file. I'm coding in raw 65c816 ASM.

My setup looks something like this:

https://nesblast.com/img/snes_hacking_setup.png

If you have basic ASM experience, the SNESdev wiki will tell you everything you need:

https://snes.nesdev.org/wiki/Main_Page

If you don't have basic ASM experience, i would start here:

https://skilldrick.github.io/easy6502/