Open up a coat and edit it. Save as .tga or .bmp at photoshop. Search for "DDS Converter" at Google and download the file of the first website. Install it. Convert your new coat to .dds, it's easy. So rename it at your own taste and put in woman or man, idk. Then, copy and paste a .elu file has the same format the coat you based your new one and rename it. Open it with hex editor and scroll down untill you find "huw_body_blablabla" and replace with the name of the .dds of your coat. Then search for "eq_chest" and change the number to "myowncoat" or any number no .elu is actually using. Open woman01 or man01.xml and put a tag looks like <ADD PARTS="partsXX" MODELNAME="myowncoat.elu">
Now go to zitem and put in "meshname" the name you gave to the "eq_chest_XX" part. There ya go.