Many common inline MS Word Fields (cross-references, hyperlinks and others) can be replaced just like normal text in O&D. If a field's text is modified via your editing instructions, it will cease to be a field and will become ordinary text instead.
Fields that do not generally occur in inline text, such as page numbers and tables of contents, fields controlled by add-ins, and various other fields, cannot be matched by O&D at this time (you'll need to edit them in the document offline and reupload to O&D).