Is there a way to switch between two folders for iTunes Media, especially for Macbook Air or Macbook Pro for limited storage? For Macbook Air and Macbook Pro, with SSD, the drive might be limited to 128GB or 256GB.  The drive also might have bootcamp for Windows, so that will further decrease the drive's size for Mac.

When the drive is closer to being full, can we "switch" between 

/Users/mike/Music/iTunes/iTunes Media


and

/My Passport/iTunes Media


any time we want?  (My Passport is a Western Digital Passport Drive with 1GB).

That seems ok as the Help in iTunes's Preferences says:


  iTunes Media folder location
  
  To change where songs and other files you import into iTunes are
  located, click Change.
  
  To change back to the original location for files (Home/Music/iTunes),
  click Reset.


This is also useful if we want to keep, say, 20GB of music on the MBA or MBP, so we can take it with us any where, and keep all the PodCast videos, movies purchased on iTunes, iTunes U videos on the external drive, so when we are home and plug in the external hard drive, we can change the path back for the videos.

(This is not so convenient, as we need to change the path for music and then for videos, but at least it may be a workable solution.  My library is about 550GB on iMac so I am afraid it may mess things up if I change it to the external drive and change it back and all the references to songs and videos, and the indexing for search are gone).

(what if we create a "symbolic link" from /Users/mike/Music/iTunes/iTunes Media/iTunes U to /My Passport/iTunes Media/iTunes U and the same for Movies and Podcasts as well, and copy all those files over?  Then when the drive is plugged in, things should work, but if we unplug the drive and take the MBA or MBP to a coffee shop, will iTunes act weird or lose the references or index to those missing videos?)
Hold the Option Key (alt) and then open iTunes and it will ask which iTunes library you would like to use.



I use one as my main library and another on a NAS as an archive for stuff I hardly ever listen to but can't bring myself to delete.