ShapeKeySwapper

Chat GPT recommended this. Just what I needed.

Lifesaver! This makes it possible to easily apply Shape Keys to the Basis:

1. Do a custom mix and make sure that all other shape keys that should not apply to the Basis are set to 0.
2. open the ‘Shape Key Specials’ menu (drop-down arrow next to the ‘Shape Keys’ list) and select ‘New Shape from Mix’.
3. set the value of the newly created Mix Shape Key to 1, open the ‘Shape Key Specials’ menu and select ‘Swap Vertecies at Shape Key Value’
4. Delete the old shape keys that contributed
5. Set the newly created Mix Shape Key back to 0 and delete it.

Done!

This is one of those niche quality of life add-ons that does exactly what it says on the tin. Well done!