Not necessarily completely impossible, just almost impossible. In order to make a full blown reskin of that unit you would basically have to make a psd for yourself, redrawing every door, hinge, and detail by hand, adding your own blank background, and manually baking and highlighting, which is very challenging to master and even then won't look quite as good as the original.
That is what it would take for a full blown skin without JR just giving you a psd to play with. However, the OP didn't ask for a tutorial in full blown skin making. He simply wants to make a more beat up looking unit with a patch on it.
First thing you will need is some sort of photo editing software. The most popular choices seem to be either GIMP or Photoshop, I personally use GIMP. After that you will need to open the unit for editing, then hit edit in explorer. Then you will want to locate the locomotive's map, should be called map1.tga. Open that with the editing software of your choice, and now we're ready to get started.
How you patch this unit largely depends on who you want to skin it for. If you're patching this unit for CSX, use the color selector and find a clean patch of Conrail blue on the unit to pull your color from. After that, use you rectangle select tool and select the area under the cab you wish to patch, then use the pencil tool and fill in that area with the color you just got. Do this for both sides of the cab, then add a small CSXT stencil along the bottom of the patch (make sure it is orientated correctly! Don't want a wild upside down stencil!). At this point the patch is done. When you save the tga file, be sure that you unclick the box for RLE compression. If you don't then the map will show up bright white in trainz and we don't want that. After that, borrow the arn numbers from a JR CSX loco and copy - paste them into the alpha numbers folder. This will replace the Conrail numbers with CSX numbers. After that, save and commit.
For NS, you can either choose to patch it black or white. For black, do not use pitch black (0, 0, 0). Instead, try 15, 15, 15 black, as it will look better in game. Same for white, instead of 255, 255, 255 white, go 235, 235, 235 white as it will not make you go blind in game. Once you have your color selected, repeat the process for patching above but with either black or white and a NS stencil. Also repeat the process above with the arn to give it NS numbers. A quick note though, should you choose to use a white patch on your NS patched unit, you will then need to go into every alphanumber(x)_b tga and use the colorify tool to turn the numbers black. Otherwise you'll have white numbers on a white patch and that just won't look quite right will it?
As for weathering, that's an entire art form in and of itself. If you search around on these forums and on google you should be able to find some basic tutorials that'll run you through the basics, but the only way any weathering skill is gained is through lots and lots of practice, which I simply do not have. I have some minimal experience with weathering and some of my attempts have come out alright, but none of them were attempting heavy weathering like what you're talking about trying to achieve. A dedicated weathering tutorial would leave you much better off than anything I could teach you. That said, I'd worry about learning enough GIMP/Photoshop to do a simple patch job first before you dive into something fairly advanced like weathering.
Hope this helps!
Sean (Souu1581)
