Can I change or remove a product's barcode after saving it?

Yes. On Plugins → Product Barcodes:

• To change it, enter the same Product ID again with the correct Barcode value and Symbology, and click Save barcode. The product keeps one barcode, so the new value replaces the old one.
• To remove it, click Delete on that row in the list.

If you printed labels with the old value, reprint them using Print, because the old code no longer points to the product.