Key_set will not help, as it is used to map on_key functions, and neither will a #define statement, as that doesn't even allow you to remap keys in game.

What you need to use is the key_for_str() and str_for_key() functions, but those only work for keyboard input. For mouse and joystick input, search for my functions on the forums: input_for_str() and str_for_input(). They work exactly the same as key_for_str() and str_for_key(), but they also accept mouse and joystick scan codes.