Lets go ahead and just make them a cosmetic. All ghost shells you’ve unlocked become a cosmetic item you can equip to change the look of your ghost. Lore wise and technicality included, there is no need for having multiple ghost shells that perform one function. We only ever put one on and switch out the mods if we need to. DO NOT try to make them “more useful”! They’re just fine, just make them an ornament!