It would have to be a change to both the spell and the item, since all the item does is cast the spell.If I could add a dissenting voice, however, it would also mean that you would be unaware that NPCs had barkskinned/stoneskinned as well. En plus, I was of the impression that the spell caused a literal sheath of living/moving bark or stone to cover the character - which, vanity or not, would cover up fancy outfits.
Not true. It is an easy edit of the spell script to account for it being cast from the helmet.
I adventure without barkskin whenever I can help it.
Is the battlefield really a place you try to pick up the opposite sex showing off your "clothing tastes?"