Since this battle engine is inconsistent, Insert cores should be attachable and detachable especially the locked cores, and may choose from the inventory. There were locked cores that is not usuable.
Locked cores should stay locked cores so that some promotional rares and seasonal rares maintain their original concept and value. Icy Chill is locked because it is an attribute that only frost weapons hold, and removing it would devalue the rarity concepts of the item.
^But certain the person who bought that item have the choice to do with their item what they want?
The person should already know it's going to be perma-locked. Sadly enough, it's gonna be their fault for buying the weapon if they wanted both core slots free.