Using the anvil_add_enchantments recipe from the test mod with identical items causes duplicate enchantment keys.

base: minecraft bow with power 5
ingredient: minecraft bow with power 5

Output: minecraft bow with 2 occurrences of power 5, and one occurrence of multishot 2

Expected an output item with only one occurrence of power 5.

I was just about to post a [Feature Request] but this issue is kinda similar.
In my case I wanted to upgrade sharpness 5 to sharpness 6, but you have no way to remove the base's sharpness 5 when merging so you will end up with both sharpness 5 and sharpness 6 in the final result.
Please add a way to edit the base's data when merging.

Edit: confused base with ingredient

This is possible in the latest alpha release (3.0.0-alpha.1).

Documentation and examples can be found around this page: https://mcwiki.siphalor.de/nbt-crafting/v3/#nbt-capabilities/dynamic-data/nbt-merging/

I'd love to hear to some feedback from you about these changes :)