That's true. The problem is more that the moves also need to account for things like whether you hit a wall/celing/spring/etc, what happens when you let go of the button (in the case of uppercut), how much longer it should be when running (in the case of kicking), and so on. As soon as these moves are "expanded" beyond what the game normally allows, it's possible to run into glitchy stuff unless it's all accounted for. That doesn't make any of this impossible though, just a bit harder!