[kiwidude]

You select the rows, you press E, tick a checkbox and click ok. One keypress and two clicks, or two keys and one click.

EDIT: Ok, I read your original post properly this time. If you get your regular expression right when you import books into your library, you will avoid having to frequently swap the author/title in the first place. Which is why there is no toolbar button for it - it just doesn't justify the space for the frequency most users need to use it.

However if you were absolutely dead set on having such a button, then write a UI plugin for it. It wouldn't be difficult.