For my college locally, we must use the same textbook for 3 years (to make our textbook rental program work, even if it's online), so it's not a big deal to make the work static for a while, then reveal a new "edition" at a later date.
However, I'll see how far I can get without an ISBN before I ask for that option. More flexibility is better!
Michelle Oja, Ph.D.
Behavioral Statistics (Statistics for the Social Sciences)