This should be pretty simple to add to the game. My suggestion is that you could simply use the mouse wheel up/down instead of moving the mouse while ‘holding’ the arrows you use to adjust part size/rotation. This would allow for much better control and also you wouldn’t have to release the arrow and click it again when you reach the edge of your screen.
You already can : just highlight the slider with your mouse then scroll to adjust.
You misunderstand, I’m talking about the cosmetic parts you use during body design such as lights and vents.