Sorry to burst you bubble but this is how it works. Yes you can unpublish a book while you make changes to allow for say errors and your eBook will disappear from sale.
However, when you republish again, all the previous reviews will return. All you can do is to put an addition to your blurb to say this is an updated version, or just leave it and await new reviews to come in. .
As for setting it up as a new project with a new title, I suggest to read the post on here while it is visible.... Kindle Notice to Block, where the author says Amazon/kindle have told them if they don't change the title back to the original, they will block the book.