I think a possible solution to this is make Tier Slot bonuses an Enchant drop with at least 10 charges. Its finite but within reason if you get an upgrade before you need to go grab another. That way you if you acquired the Helm Tier Enchant it can be applied to any new Helmets you pick up. Can also get the exact stats you want for that slot as you pick what gets applied rather than relying on the item it comes with normally.