This page will discuss the nbt_items.json file in the mod's config folder.

Purpose

The file is a map of items to a list of NBT tags. When an item is added to it, along with some NBT tags, the Transmutation Table will be able to remember that item's NBT, but only the keys listed.

Here's an example entry:

"minecraft:enchanted_book": [
    "StoredEnchantments",
    "RepairCost"
],

The item we want to store the NBT of is minecraft:enchanted_book. But we don't want to store NBT data such as an anvil-set display name, so we only list StoredEnchantments and RepairCost. This means that, for example, transmuting two Protection 4 books, one with a custom name and one without, will make the player learn the exact same item. However, two Protection 4 books with differing repair costs will be remembered. (The balance reason for this is to prevent the player from transmuting and instantly taking out an enchanted book to remove the repair cost penalty.)

Important Notes

The file supports tags! This will make the Transmutation Table remember this NBT key for all Shulker Boxes.

"#c:shulker_boxes": [
    "BlockEntityTag"
],