https://github.com/rusefi/fw-custom-example is an example of a custom rusEFI firmware repository. Just fork it, edit ``.github\workflows\build-firmware.yaml`` file, rename ``compile_XXX.sh`` with your board name and you have full control over default tune, connector mapping etc!
https://github.com/rusefi/fw-custom-paralela and https://github.com/rusefi/fw-custom-core8/ are the best example as of right now.