A coating applied by PVD changes the first few microns of the metal its applied to, that's why its main use is to provide a harder wearing surface in high friction situations. To remove an existing coating would need enough material removing that it would be difficult to keep the original shape untouched.
Good coating companies won't usually accept a product that has had a previous PVD/PACVD coating, as even if you can remove enough metal to get rid of the original coating completely, the results of a second coating can be unpredictable, most coatings need the item to be heated to about 600 degrees!
If you did manage to get it all done and it came out ok, the costs would more than getting a new DSN pvd case anyway.