It's not like permanent, but temporarily changes whatever -including makeup, tattoo, costumes, inner armors, hair, colors, etc.
Use it whenver you want to show it off in town, perhaps. I used it to see how I would fuse my costumes.
@ruzrica If your in town only you can see it, the only time other people can see the changes you've made are when your hosting a boat/dungeon.
Oh, I didn't know about that =P, but won't matter for me, since my purpose is just to see how the matched costume look like.
Otherwise, unfortunately I don't know the other way to hack inner armor, sorry.