Nothing Left to Lose:
Thanks for your suggestion. I've decided to export the worksheets into MS Word as tables and use the redline capability of that application. I believe that will get me where I need to go. But I do appreciate your recommendation.
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It worked as I expected though there were issues bringing the table back into Excel. New data does not align correctly with the existing format and attempting to manually move the boundaries does not work.

So I will try pasting into Notepad and cut and paste into Excel from there, or create a comma-delimited file and import that. Subsequently, I'll manually highlight the changes. There's not too many, so it won't be onerous.
Still, this is all pretty much a kludge.