For re-skinning the main tool is a graphics editor.. Anything from Abobe PhotoShop (costs lots) down to a myriad of freebees like IrfanView, Gimp, Paint.net. I use PaintShopPro 7 (I've had it for years) and it is able to do almost everything I need.
If the asset your wish to re-skin only has *.texture files as the images, you will need my Images2TGA tool to convert the Trainz textures to targa images.
If the images are jpg, bmp, or tga then you can get straight on to changing the colours and lettering. Any reasonable image editor should have appropriate tools or commands to do this.
I suggest your copy any images you wish to edit to another file name to act as backup if you mess up the originals.
So the order of work to do a reskinning project could be:
1. select the asset (loco, wagon, scenery item) that you wish to reskin..
2. Using Content Manager "clone" it. This will make a new asset with the same contents but with your user number in the kuid. You can also edit the name of this new asset to suit yourself.
3. Browse the cloned asset edit folder and find the texture images. If they are *.texture only you will have to convert them to TGAs. If you have installed my Images2TGA tool you should be able to do an "open with" edit in Content Manager. (TS12 only feature in your case) Select your new asset in Content Manager and right click on it. From the "Open With" menu choose "Images2TGA.bat" and the converter will scan the asset and convert any *.texture files it finds to *.tga files. It will also make the necessary texture.txt files to connect these new images to the game.
4. You should now have some images that you can edit with PhotoShop or whatever.. I don't propose to tell you how to do this as it varies from package to package.
5. When you have edited the images, just save them.. don't change the filename, size or add any file compression features to them.
6. You have two choices to look at your handiwork.. You can commit the new asset into the game and look at the asset in surveyor,
or you can view the asset with a mesh viewer such as my Trainz Mesh Viewer. If you choose to use a mesh vewer, you will have to manually delete any *.texture files, or the viewer will choose those before your altered images.
Note that if you committed the asset into the game and then re-open it the *.texture files will no longer be present.. This is normal because Trainz Content Manager cannot re-commit trainz binary textures.. It uses the images and texture.txt files to build new textures. ( that you will never see in content manager)
I hope this can act as a starting point for you in your re-skinning projects.
Others with more experience at this than myself may wish to add more tips to help you along the way.
Once you have mastered the basic skills you may like to tackle more advanced re-skinning where larger textures can be used to improve detail and where the alpha channel of the images is used to have transparent, semi-transparent or masked details.
My Trainz tools and tutorials of their use can be downloaded from my
PEVSoft Downloads page.
Have fun..