Sometimes the answer to a question is to try it and see. When you use
Save Book as > RTF the message below is shown.

- SaveBookAsRTF.png (29.7 KiB) Viewed 906 times
So, yes, in Word you can update the Table-of-Contents and the Index.
However, you cannot transfer the whole Word document back into a Free Text page and retain all the formatting.
Character fonts and line justification are retained but images, page breaks, Chapters, Table-of-Contents & Index are not.
I don't understand why you want to transfer back into the FH Book. Just save, edit & print the Word document.
Presumably, we are discussing the wording in Narrative Reports that you want to adjust.
The are several ways in which the wording of sentences can be customised.
In
Tools > Fact Types... each Fact can be edited and the
Sentence Template changed to make them less repetitive.
However, that default sentence will be similar for all Facts of the same type.
On the
Facts tab of the Property Box, the
Sentence for each Fact can be customised specifically for that one Fact.
Another option is to use the
{note} code in any
Sentence Template and then whatever is in the
Note box for a Fact will be included in the sentence and thus can be different for each Fact.
The advantage of those techniques is that FH remembers the changes and will include them in all subsequent reports so you don't have to repeatedly edit the same sentences every time you recreate the Report or Book.
See FHUG Knowledge Base
Narrative Report Fact Sentence Templates for further details.