Good to see a book about this, a topic that's been around some time, but never formalised. Not aware of any formal methodology for safely changing code once it's in a working system, so this sounds like a welcome addition to any conciencious coder's library. Code Complete (MS Press, ISBN: 1556154844) by Steve McConnell is also an excellent work which would probably complement this one. Although it concentrates more on getting the code right in the first place, many of the same principles apply, though it does not present a method for safely re-writing code. Maybe one to send to your third party application provider when your new $100,000 app. starts performing like a dog 😉

Jon Reade