Rare Transmutation Stone – the ability to transmute your armor with the appearance of an armor which is of a different class.
So, you could have your warrior wearing what appears to be leather chest and leggings, and have armored limbs, with maybe a light armor mantle.
Make them pricy like 500 gems per stone, I don’t care. I just want to see if it could happen. 
to much clipping would happen.
It would look very horrable
There’s already a ton of clipping with compatible armor anyway (try wearing any leggings of heavy armor with strong banded heavy armor legs for example, or draconic leggings with the exotic armageddon legs). Some combinations of light/medium/heavy armor do work as I’ve seen in preview, so it would be up to the person transmutating it to see what works best.