How to change URL alias when importing books?
Have you created a vocabulary for these books?

If not:


Create a vocabulary, e.g. "books_category" 
Add to your content type field, e.g. "books_category" (field type: Term reference), choosing the vocabulary you previously created as reference


After that, click at replacement patterns (admin/config/search/path/patterns); choose group "Tokens related to individual content items," or "nodes"; you will find a group of patterns related to your "books_category" field. 

I assume you installed the Pathauto module.