For DRM'd books I tend to edit the book's metadata in the Calibre/device window.
SO allow SonyLibrary *spit* to add the book to your device. Then close SL. Open calibre. It should see the devive. If you click on it you'll see all the books on your reader (not your library). You can then edit normally.
It's worked for so far with ADE stuff. I'm non-US so can't use the Sony store fortunetly.