Hi,
You can save the bookmark at any stage of the report navigation. When you freshly logon to Portal, you can select that bookmark and it should ask you to confirm already saved Variable entries-->Execute-->It will show you the exact bookmark you have saved before. All this can be done with that Bookmark button with standard command.
You are right, that if any new changes in the report are made, thjose will not be saved in the old bookmark.
Regards,
Suman