I am at the point in Amazon KDP where I am wanting to see a preview of my novel. I do not have an ISBN number yet because I am still only wanting to preview and not publish. Amazon asks if I want a free ISBN number from them or if I should provide my own. If I choose to have Amazon provide the ISBN, am I stuck with it or can I back out and later add my own? The reason for this is I cannot upload a manuscript to preview without a valid ISBN number.