/macro book # (changes the initial book)
/macro set # (changes the page within the book)

And you can put both in one macro and bounce your usefulness around like a Neo Anderson. My SMN needs one book for each subjob, and an extra book so I can gear up to the subjob, cast subjob spells, and the ability to siphon any elemental. If they keep coming out with more avatars, it may come to the point where I need 3 books for each subjob to SMN.