Also made a post on this myself, called " Give the ability to exchange Core Forged for Draconic Set Bonuses ". The fact that you can’t makes absolutely no sense because the purpose of getting a second set of tier is for your off-spec. Not having the ability to go back and forth is just bad game design and causes unnecessary friction.
The consequence of this is having to re-enchant the piece of gear, some of those enchants are not cheap.