To easily move some of your library...
- iTunes prefs - Advanced.
- Make a note of the current iTunes media folder location (default is /Music/iTunes/iTunes media/).
- Tick Keep iTunes media folder organized.
- Tick Copy files to iTunes folder when adding to library.
- Set the iTunes media folder location to the external drive where you want the files to be.
- Click OK.
- Select the files in iTunes you want on the external.
- Right click - Consolidated selected items.
This will copy everything selected to the location set above.
Now you can delete the TV shows from /Music/iTunes/iTunes media/TV Shows/.
All metadata will be retained.
After you are finished, go to iTunes prefs Advanced and reset the iTunes media folder location to the location you noted in step 2