KDP phone support is shockingly helpful. I call them frequently and they're often able to accomplish stuff for me which doesn't have any sort of DIY interface. I call them at least once a month for something or other and am always impressed.

One of my friends just released a new edition and was able to it up and set the new version as canonical, which preserved the ratings, reviews, etc. I haven't done it myself and may be muddling the details, but I'd definitely call KDP support before throwing in the towel.