If you have synch'd your media you could always edit the synopsis in Media Files Sync.
If you've got a lot of movies this would be a real pain.
If synch'd you would probably have to turn off mediaupdate, edit this synopsis in Media Files Synch, delete the id3 tag from the /usr/pluto/diskless/XX/device/public...whatever HDD location.
Then turn mediaupdate back on to get the modified id3 tag recreated on the HDD.
A bunch a playing around but an option.