By installing this module, in product variant screen you will able to add multiple EAN for a product under Sales tab. Here you will find a button "Generate EAN Code". Clicking on that, you can generate EAN manually anytime. In case of multiple EAN of a product, lowest sequence EAN no. will be considered as Main EAN for a product. You can't modify main EAN inside the product. Just change the sequence inside multi EAN section, and lowest sequence will be set as main EAN for that product automatically.