You are an evil, sick, twisted individual and should be banned forthwith from the Modelling community. Joking of course lol.
Knowing the Pullman’s, I would imagine you would just need to remove the corridor connections, buffers, handrails, and glazing. The Pullman’s don’t have large amounts of external seperate details so it is one of the easier repaints.
Opening up the coach is fairly easy. 4 clips at the corners, and a clip in the centre of each side too.
Are you sure you wanna do it with a brand new unused one? Surely a 2nd hand one would be a better option for