How to move part of iTunes library to external drive

Copied the  answer by Chris CA from Apple Support Communities thread. 

To easily move some of your library...

1. iTunes prefs - Advanced.
2. Make a note of the current iTunes media folder location (default is /Music/iTunes/iTunes media/).
3. Tick Keep iTunes media folder organized.
4. Tick Copy files to iTunes folder when adding to library.
5. Set the iTunes media folder location to the external drive where you want the files to be.
6. Click OK.
7. Select the files in iTunes you want on the external.
8. 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.
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