Antonyms for "according to the book" can vary depending on the context. Some possible antonyms might be "outside the book," "not by the book," "beyond the book," or even "ignoring the book." These antonyms suggest a deviation from the prescribed or expected course of action or thought as laid out in the book. Instead, one might be improvising, disregarding, or innovating based on their own intuitions or needs. Antonyms can sometimes shed light on their opposite by highlighting the ways in which something is not, and in doing so, illuminate what it is.