How to change init caps to all lowercase IN INDEX ENTRIES

Hi. using ID 20.4.1 under Windows 11 (long may it wave).

I have rigorously indexed a client's document (which I also laid out). The client has a tendency to use "Teutonic Capitalization in All Things and for many Important Nouns." Naturally, when I indexed their document, I indexed using these important capitals... because they were important to the client... but I also put things in lowercase when they were concepts or topics not specifically capitalized in the product by the client.

The client objected to some index entries being in uppercase and some in lower... suddenly craving a consistency they did not employ in their own product. Anyway, now I have an extensive index that -- according to Chicago 17 -- needs to be rendered in lowercase except where it's a proper name, etc. (Mea culpa for not consulting Chicago beforehand and advising the client appropriately.)

Is there an easy way to find each index entry and render it in lowercase (except, of course, for those proper names etc.)? Like... search & replace, maybe a GREP...? Certainly, I can manually edit down the list provided in the Index window.

The simplest way to take care of business would be to turn the Index-only typestyles into forced lowercase... but there are those pesky proper names and the etc. that still need to be uppercase (and that doesn't do anything about how the info was entered into the Index dialog to begin with). <sigh/>

Thanks as always to the community.

-j