So each chapter is a separate doc?? If so, you could maybe merge them all into one big document and make your notes as a long header (which you can later delete), with specific references to chapters. But if it's 90 chapters long, depending on the length of each chapter . . . that would be a humongous document . . . and I don't know if Word has a character limit on document length. So that may not be an option, if it even addresses your concern anyway.
Other than that, it seems like you're looking for a way to globally open multiple documents, and then making the change in each one automated. And if all your changes are different for each chapter, I don't know if that would be possible without tediously doing the same thing anyway. Though maybe there's a macro you could write to do that.
I'm not real proficient in Macro language, so if a macro is the solution, maybe somebody else will jump in here with the specific guidelines.