The main ebook file you have created in MS Word is sacred. It represents the writing of a document at a particular time in history. You should now save that document and never from this point forward use the F9 key to update fields. Save the file under a new thought or child thought if you like and put it aside. Now copy that file and link it to the main MS Word thought in your brain and use the copy for any further revision activity.
Name versions
That very first document should be saved using the title of the book and the date of production. The copy you just made should have the title of the book, date of production and if it is on the same day the hour of production.
Changes
Any changes you do should not be made to the main MS Word document file. You have created the document using a system; you should use the system to make updates. By using the system to make updates you then keep your text chunks up to date and therefore making them useful for other texts.