[cxr]

> it may be a reasonable expectation that a text-book would be 'correct', and so receiving updates would be appropriate[...] Of course this should be consensual

It is implicitly consensual—when the consumer chooses to buy/download the newest edition. Don't try to "change" what's an an ebook, though. (Not that it's even possible.) Make new editions available if you want and allow the reader to decide whether to go for them. Otherwise, it is not consensual.