I work so long on Mac, that I use the clipboard shortcuts Cmd+C and Cmd+V just like I did Ctrl+C and Ctrl+C on Linux and Windows earlier. (Not mentioning Ctrl+Insert and Shift+Insert a lot earlier.)

I looked at bindings/default, which is ready for customisations, but the naive approach replacing CTRL_C Dit_copy with CMD_C Dit_copy would not work, because it would lack support in sources, where macros recognise only CTRL and ALT.

What would be the best approach to get CMD among the supported key modifiers?

I do not understand autogen/automake, but can code in C/C++.