I don't know much about character model modding

But retexture only will make it very weird in-game

I was thinking more about putting the 76 on the back, and the white on the front, the black on the sides and the sleeves, and the blue on the collar and outside of the sleeves, the red on the top of the gloves, and the black undershirt/thing.

Not just pasting 76's closed jacket texture over the texture of Rusts open jacket, more recreating the look of 76's jacket on Rusts jacket.

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Something like this poor photoshop job http://imgur.com/ZF2M9Hu