Would it be possible to build a template that will be able to change the button text within the shortcode, taking the text as a parameter, instead of picking it from the general settings "Buy at" field?
Something like:
[atkp template='12345' EAN='B0BCP3JP6F' buttontext='Buy Kindle'][/atkp]
[atkp template='12345' EAN='0593593804' buttontext='Buy Hardcover'][/atkp]
Kind regards.