Changing Product ID Type from UPC to EAN

Hoping someone can help. As of Friday we have had a new error displaying on the product ID section of each SKU.

We have set up our products as UPCs, however our GS1 Barcodes are actually EAN codes which means they are a digit too long to be UPCs.

Amazon are telling us to change the product ID type from UPC to EAN, but when you go to edit, the fields are locked. They are saying we should do this via template upload. Would we have to do this for each category, or is there a quick way to do them all at once?