crafting_transmute recipes that apply enchantments will overwrite the input item's existing enchantments.

Create a new world with the attached data pack installed.

/recipe give @s minecraft:enchanted

If you craft this recipe using an enchanted pickaxe, the resulting golden pickaxe will not have any of the input iron pickaxe's enchantments. They will instead be overwritten with only Fire Aspect I. I expected the behavior of this recipe to add Fire Aspect I to the enchantment list without removing any pre-existing enchantments