Darth Venal said:but you're forgetting, the fact that Han says they are conveying parts and supplies is the reason Piett and Vader know they are lying, so the shuttle should stay as it is.
If we want/need to vary the overused shuttle design, it's far simpler to alter the Emperor's shuttle as it's only seen as a matte painting and then a couple of shots of the terrible studio mock-up. That can be replaced far more easily.
I don't know where you got that idea from.
Piett is sceptical because the code is older and he is possibly picking up on Vader's hesitation (people have been choked for less).