Hi,
Yes, you can have e EAN for each variant. You can either use the "product code" field for that, or create a custom field of the table "product" via the menu Display>Custom fields to store that.
There is however no system to easily update the stock via a URL.
It's possible via a CSV import but it's usually done to import all the products at once, it's not adapted to be called by a URL for one product.
PS: please open a new thread when the question is not directly related to the topic.
