Can I have two iTunes libraries open at once?

I would like to create multiple iTunes libraries and store some of them on an external drive to free up space on my primary HD - for instance, a separate iTunes library for songs I listen to only on occasion, such as holiday music. I don't use it 11 months out of the year, so I would like for it to not use space on my SSD.

My question is: if I do use multiple libraries, during those times I want to use the other libraries, can I have that open side-by-side with my existing/primary iTunes library? Or is it a one or the other deal?

Any other tips/best practices for situations like this?