The answer to this is yes, you can indeed do that.
There is a row of three buttons just beneath the main image in the library browser - one colored blue with a red stripe, one colored solid red, and one that looks like a trash can.
The button that is colored blue with a red stripe and a plus sign will insert the tracks from the selected composition in the library browser into the current project composition, maintaining all of the original tracks.
The button that is colored red with a plus sign will close the current project and open a new one with the composition from the library browser.
Clicking on the button with the trash can will delete the project from the library browser.