Q: I am revising a book. Does it require a new ISBN?
A: A (substantial) change of text requires a new ISBN, and if revisions have been made the back of the title page should state that the book is a revised edition, and the new ISBN should be printed there.
5.1. General
A separate ISBN must be assigned to every title, or edition of a title by each publisher, but NOT to an unchanged impression or unchanged reprint of the same title in the same format by the same publisher. Revised editions require a new ISBN. A price change does not call for a new ISBN. Changes of the format induce a new ISBN. The same title being published in a series and individually is treated as two different editions.