Just keep in mind when changing IDs that you may want to verify that any links in the ebook that use that ID as an anchor in an href, get updated properly to reflect the change.
It doesn't matter what you use for an ID (though I don't believe they can begin with a number) ... but what you use does matter for the rest of the epub that may want to use that ID.
The changes should propagate automatically when using something like Sigil, but it doesn't hurt to check.
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