I suggest that multiple functions should be able to be assigned to one key.
Due to the recent shield bash/dash update, I've ran out of keys to conveniently use. I would like to add my move forward and modifier to the left/right mouse button, so that I can simply press Z or X to dash or bash while moving.
Certain movement related keys do support multiple things assigned to a single key.
But to clear your problem, you don't need a modifier key to use a dash or bash. You can assign them to a single key.