I think it was a horrible decision to release the book now. He should have waited until the trial is over. It's just fodder for the prosecution. Reports of the book's repeated claim of the reverse race card being played will be picked by anti-Zimmeran sites and spread around, potentially increasing the prejudice to the jury pool.
Just on principle, that's a sad reflection on the state of the law, and race relations, in this country. Very directly, its an admission that criminal law can successfully be used to extract illegal revenge. If that were not so, your fear would have no foundation. The illegal revenge, first enabled by the state, comes from increasing the number or resolve of potential stealth jurors. I haven't read the book, but I speculate that it points out that the prosecution of Zimmerman is lacking probable cause, and was driven by widely reported false claims.
I think the damage (to the state of the law and race relations) was already done, book or no book. But the state will never be able to obtain a conviction. I think a clear majority of jurors will follow the evidence and the law.
You are right that the revenge-minded folks, and they are numerous, will be energized by this book. It's hard to tell if that improves or damages the chances of a stealth juror getting by the court's filter. It takes only one stealth juror to cause a hung jury.
At the same time, the book also energizes those who have been viewing the case with more or less clear eyes. I have never been more angry at what the political players have done to an innocent man, using what used to be a steely-eyed and fair institution. The state, and its court system, have become the enemy of the people.