Changing Sword Hilts/Handles

Ok, say I have a sword with:

Fire Dmg 15-22
Damage +12%(vs Hexed foes)
Armor 7

and i wanted to change the "Damage +12% (hexed foes)" part to something like "Damage +12%(while enchanted)" w/o changing the Fire Damage. is there any hilts or handles that only changes that single part?

The damage +12 vs is a natural ability of the sword. A weapon can have 2 upgrades (one of each type)which can be changed and up to 2 natural abilties which can't be changed.