According to [1] if the product has an EAN/UPC/ISBN barcode, it gets commingled, but vendors can put a sticker over it with a different barcode to prevent commingling.

Or the FBA label service [2] can apply the stickers for you, at 0.15/item

[1] https://services.amazon.co.uk/services/fulfilment-by-amazon/... [2] https://sellercentral.amazon.co.uk/gp/help/external/G2004837...