skins are done by editing the DDS. file of the model.
This is a image file which for photoshop or other stuff you might need a plugin to use.
Go to RO SDK, find the "ger_rifleman_tunic", export it to say my documents, then it exports a copy of that texture to your documents.
Find the folder in my documents and attempt to open it with your image editing software.
It opens up a picture which all the detailed bits are the "skin" of the model, that skin wraps its self around the model.
BE WARNED, its not as easy as you might think, if you dont make it look nice, it will look like utter shite.
Once you have edited the DDS file, this is as far as i got, you then save it, open RO SDK, import that texture. Then apply it to the model.