I'm pretty sure this is pretty much impossible - you can't add on to a skin unless we would make a skin for every little bit of clothing in every possible manner - which would be a rediculous amount of work if we want an even decent amount of variety in the clothing.I'm not entirely sure if it's been suggested in a previous post, but changeable clothing apparel like in standalone would be awesome.
Perhaps shoes that allow you to run faster or lower noise of footsteps, clothing that will allow more maneuverability but make you colder, etc.