Hello.
You can't add/remove items from Looter using LUA Script neither change how Looter works internally, like custom behavior.
I don't believe that 3368 is rare mace id... If you have two items of same kind like a common mace and a rare mace OR rare and epic, etc. Then you can find out its IDs moving them to your belt slot and running this code:
I MAY BE WRONG, but I believe that common, rare, epic, legendary, ancient items shares the same item id, however they can have a custom attributes or something then that attribute is what differentiates the "rarity" of these items.
So I believe if you add a mace to Looter, it will loot all maces: common, legendary, etc.
At the moment it won't be possible to do such thing, because bot doesn't have the skills to make this distinction. I don't play this server, so I don't have access to these items (different "rarities").