You should refrain from making edits while your book is being edited. However, after you have received the editing back and before you send it in for designing, you can make additional changes. Once your book is being designed, you should wait until you have received a pdf file for review from the designer. You can make changes at this time and up to the first printed proof you receive.
Keep in mind that the later in the process you make changes, the more costly it can get for you.