Idiotfaic, you can do this by reconfiguring the input event layer of your OS or the input event translation of your GUI.
However, it does not make much sense, because if you bind move and fire to the same key, you would also need to have extra keys fr movig and firing, in case you don't want to it at the same time; and if you already have two keys for this, you could also simply press them at the same time, instead of using a third key for the same functionality.
Also, some bindings (the ones that would make sense, like move and face in a certain direction for example) can already be assigned to the same key (and before the patch that broke it and hopefully after the fix, joystick axis, too).