@edwinattaway The technique does work... it's the 'restore' part of the standard way users back up (copy out) and later restore their bookmarks file in their profile folder. It assumes only that the bookmarks file being copied in isn't corrupted. The only question is whether the user wants instead to merge the original into the current bookmarks file (which this technique doesn't do - it only replaces the current "bookmarks" file in the profile folder with the copied-in bookmarks file).
Yes, it does work. I pulled an old backup that I could compare with the current one. I did as you said, and as I suggested. I have the old bookmarks on my bookmarks bar and the "Bookmarks Bar (File)" after I imported - as I suspected. Now, I'll just drag the ones not in my February 5, 2018 backup image. I didn't mean to imply it wouldn't work. Unless I have done it, I can only support what I "think" will work. Now, I know it does. You only said, "Have you tried..." That didn't sound definitive, to me. I should have read into, "Note: The copying should be done with Opera turned off." was the "definitive" I was looking for. My apologies.