We already have an import excel functionality for this which you can use for deleting all the barcodes at once. Use Import class: 'Promotion Assortment - Item Addition' for the same. You will find a provision where system will ask you behaviour, i.e., Specify whether to clear the existing assortment details and then populate the new ones or just to append to the existing ones.
If you want to add multiple barcodes, then add, else remove.
Kindly provide some more inputs to understand your requirement,
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