I believe the book will be released along with some of the new models during the month of november. So, I would pre-order now from Derek to make sure you get a copy.
But, I would think it would be as we have ruled in the past that the current book is legal as long as there are no issues with players retaining a copy. You'll have to have it with you though for obvious reasons. The GW website says the book is coming out the 7th of this month. That should be more than enough time for everyone to get used to the new rats.
