For many (but not all) cores, you can use the core input remapping feature
You the “Core Input Remapping Option” in the Quick Menu after pressing F1 when the core is running?
I can’t change the Mappings because i use a Keyboard, not a Gamepad.
For others, you can use configuration overrides, as described here:
maybe i’ve understood something wrong: i create a new core specfic config file in lets say .config/retroarch/Snes9x/Snex9x.cfg. in the example file for nestopia there’s something like “input_libretro_device_p1” in the config? whats that? in retroarch the buttons have different names, for example “input_player1_b”. i don’t know what to do to switch the binding for input_player1_b and input_player1_a only in snes9x core.
i also can create a remap file in snes9x subdirectory, but changing the binding has no effect after restart the core.