If you purchase the books from Amazon on your author's discount, what you do with them is your own business. But if you used an Amazon-provided ISBN to publish the book and then, have the books printed elsewhere for sale in a bookshop, you'll have to obtain and use another ISBN for that edition.
KDP authors are not allowed to diversify to other ebook sellers but I can't see anything to stop us selling to bookshops.
Does anyone have any experience of this, please?