Just started modding couple hours ago, but I believe Sench posted the answer in this thread:
So,
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Create a child of the official Amarberry
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Move to your mod folder
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In your “PrimalGameData_Test”, check out field “Remap Item”. Point the “from” to the official Amarberry and the “To” to your child Amarberry.
I’ve not tested this but I really hope it works.
Edit: it does.