Illager Invasion is a "vaguely vanilla+" mod I like that also has an over-max-level-enchantments mechanic, so I decided to create an addon that lets you craft Ancient Tomes in its Imbuing Table. Typically this table is used with a tool with a max-level enchant, a max-level enchanted book, and a Hallowed Gem (item new to Illager Invasion) to create a over-max-level enchanted tool. With this addon, two max-level enchanted books of the same enchantment can be combined with a Hallowed Gem to make an Ancient Tome.
It also has a config option to disable the Imbuing Table's usual functionality (which isn't the case by default), but I would recommend turning off "allowNormalUsage" if you want to require users to use Ancient Tomes in an anvil in order to obtain over-max-level enchantments. I'm open to considering adding more config options, but for now this is all it does.
As of writing, I am awaiting approval, but the downloads will be here:
CurseForge
Modrinth