So you want to be an affiliate for multiple shops.
Once you have created an affiliate account for a shop, that is all you need. If you find another shop that you would also like to promote and become an affiliate for, simply go to the new shop's login page for affiliates. Use your current email address and password to login. This will automatically associate you with the new shop as well.
You should then see all associations with your shops within your affiliate portal. (You can also click here)