You don't say what reader you have. PRS+ now lets you manually set the new tag. The
Order Books utility also lets you set or remove the tag also very easily without having to change your firmware if you'd prefer that method.
Or if you can find which file your reader stores the info, it's a simple matter of editing the file. For the x50 series of readers:
Open the file "database\cache\cacheExt.xml". Each book title needs
opened="true" added to it. Change true to false if you want the new tags back on all books.
But again, depends on what reader you have.