What speeded up the process for me immensely was discovering TinyHexer, my hex-editing tool of choice. It has a pop-up window that can provide decimal conversion on the fly, and lets you type in decimal amounts rather than hex code - it even gets the inverse-order correct! Prior to finding that gem, I had to use two tools, one to do conversions and another to hex edit, very cumbersome.
To change the shape, such as shortening a unit (or lengthening a boiler as I did in my Class A), you don't have to bother with remapping faces; you're just tugging the corners of the faces around. Of course, this will warp the skin a bit, think of the newsprint image on a piece of silly-putty when you stretch it; you'll just have to tweak the skin file to look right. I suppose one *could* remap the skin coordinates, if you want to avoid having to stretch or squish the skin file's components, but I think it's just easier to squish in the skin file.
If you wanted to do more than just move existing points around, such as perhaps adding an extra radiator grill or other feature not present in the current model, then you get into modding both the points and the faces. It's not hard, either, just tedious, but with TinyHexer it's at least plausibly achievable. I did this for my SD40 - I took the GP-35, spread its two radiators out a bit, then enlarged the center third radiator to match the others, and remapped its skin coordinates to match the other two.
=Winchester, Paston & Portsmouth=
====== We Provide Pride! ======
Also notice the difference between the .DDS skin (Lead Unit) and the .TGA skin.
