1. Locate the cars in CM. I'll use kuid2:4524:300010:1 (TTX 53 Maxi-IV A) as an example.
2. Right click, clone it. This is a good habit, in case you mess things up you still have the original intact.
3. CM should automatically display the clone. Press CTRL+SHIFT+E.
4. Open the mesh body folder, and open the map1.tga file. (Ta-da, here's where all the fun bits happen.)
You edit this just like you would any digital image or photograph. If this was 10 years ago you could even get away with using Microsoft Paint. Let's use this
BNSF set as an example, it's not exact but it'll do for now.
A big part of texture work is research and sourcing. Please don't use an airbrush to paint your logo like some people do. We need a proper one,
which I've found here. Save the image. Now, you see, the reference image calls for a white logo, not orange and black, so we need to process this first. Open the logo in GIMP.
Color range, select white/negative space, delete. Color overlay > white, don't preserve luminosity. Save as PNG.*
The reference image also calls for "BNSF ######" numbering. This JR car has automated running numbers (ARN). If you're reskinning a unique car you can remove ARN altogether and skin 1 car number. However we'll leave that intact for now - it's pretty advanced stuff. We're going to remove the black rectangle and replace DTTX with BNSF. You'll need the appropriate font,
which I've found here. Use that font also to replace the A/B/C set markings.
Copy orange, paste over black, clone edges.*
Patch tool DTTX text, type BNSF over it.*
Ok, so far so good, but the color's all wrong though. It should be dark red.
Adjustment layer > black and white > maximum white. New layer, paint red, blending mode multiply.*
There, done.
*Quick notes. WIP.