The books are not items per se, but codex that can be represented as items. They are defined in his own .codex file-type, and they have his own unique ID that define them. To make a patch, you only need to use that ID.

The patch, will be in the next form:

Were <id> is the unique ID of the codex that you want as a book, and <category> is the tab in wich you want the book to appear. In the base mod, you have three categories, novels, manuals and history, but other mod could add his own tabs.