@jbodders2018 Hello, I m facing the same issue. Have you find a solution?
Config file overrides for RetroArch are explained here and are probably more inline with what you're looking for. It includes an example for per-ROM configuration.
I just made one too :) its pretty darn sweet!!!
@kevreh Just keep in mind, the two methods conflict with each other, so I think GPIOneer turns off RetroGame. You can't use both at the same time.
I'm keen to hear how this turns out too. Using a Xin-mo controller in my Raspi powered arcade cab with uae4arm.
I was hoping that the joystick only games I played as a kid would be good to go as far as far as mapping was concerned..