hmmm... after some reading online (not in my manual) it appears you can add a file with the exact name the generated file would create then FM will use that file to create the TOC. Alternatively, it appears one can import formats from another file/template into the generated TOC to satisfy what one is looking for.
I would still welcome anyone else's comments about this and/or to correct my thinking above.
You're correct for both cases. Either import the the existing TOC files formats into the currently generated TOC (and re-genreate the TOC) or copy the current TOC to be the name of the FM book file with a _TOC suffix and place it in the same folder as the FM book file, e.g. for myBook.book create myBook_TOC.fm by copying your existing template TOC and place it in th folder myBook.book reisdes. Then re-generate the TOC.