The only way to do this without Paintshed is to use a graphics program to open the texture files and alter them to your liking. Once you save the item and commit it with a new kuid, you should be able to enjoy your reskin.
Yes, it's more complicated than that really, I suggest searching the forum for reskinning tutorials, and going from there. Good luck.
Theyre arent to many out theyre some old ones on dls
its a basically a good paint program and a lotta talent.......
I do believe some payware sites do have the meshs that you can purchase...
that can be painted but with restrictions.........
also a couple freeware have kits......
Also will find with some hunting of old skin versions in the CMP reskinners tended to add a blank copy to a version they did but its a lotta hunting....
For your own use you can clone any loco you want and reskin it. Alternatively, find a loco you like and then email the author for permission to reskin and upload to the DLS.