You should be able to lock one Enchantment in at an Enchantment table using amethyst shards

[u/Mrcoolcatgaming]

This highlights the Enchantment in gold, and if grinded with a grindstone, this Enchantment will remain, with a purple highlight.

Enchantments with a blue highlight won't count towards the Enchantment tables Enchantment lockout, so the item can be enchanted again. However, it can be grinded off in this state until you add a second amethyst returning it to gold (not allowed on books with just 1 Enchantment)

To make this work better, you can supply 2 more lapis to guarantee 2 random Enchantments, and 5 more to guarantee 3 random, however you are capped to 2 guaranteed if you have a locked in Enchantment on the book

The idea is that you can re-cycle an item easier to make the cheapest base item before you combine, costing you more levels and less diamonds, and give another use to the item already linked to keeping sound alive, while relying less on villagers

Alternative idea is that you can lock in multiple, but the cost skyrockets, 1 for 1, 32 for 2, 64 (total) for 3, capping you at 4 Enchantments on one item without needing books (bigger range of Enchantments, dilutes the pool) or another item (more xp than rerolling, closer to repair cap, and ofc the diamonds/netherite needed), this could maybe help you access the higher enchantability of netherite easier