I'd like prototypical NH streamline cars in N, but all that's available are Rapido's coaches. I'm wondering if I could hire somebody to print out partial sides of other NH cars with 3D printing, and I can switch out the sides on stock Rapido coaches with them. Not looking for a whole new shell, or interiors, just a change of sides. In fact the replacement part could be just the area above the belt line, meaning the windows and the fluted area above them. In that case, a filler panel would be needed at one end of the side to cover where the one boarding door would be removed. The car to be modified has only one door and the window sections on a side cut away, with the new replacement window section and filler panel fitted in the space. Most of the car side would then be stock, making the modified car less conspicuous in among the factory models.
Obviously plans would be needed, but I've a NH book that has shop drawings of all the 8600 series cars. This would be a very flat project, with the only raised details the fluting above the windows and below the belt line on the door replacement section, so I assume it's not a complicated production.