Simply stated, that is not enforceable. There's no meeting of the minds. Otherwise, there would be no certainty. Can you imagine if one party really could change the terms of a contract at will, particularly the way people typically don't even read contracts?
I'm not so sure that's true, at least with respect to what we are talking about here. Certainly Prosper can't make enforceable retroactive changes to the Notes and such, which is why their failure to sell defaults to JDBs is a breach of contract. The reason being that once a loan was made, it was a completed transaction, subject to the rules then in effect. But it isn't obvious to me that Prosper can't change their rules about using their PM system, for example, and expect anyone choosing to subsequently use the PM system to abide by those new rules. Under that theory, using the PM system would constitute implied acceptance of the then-current rules. And IIRC, Prosper does make reference (with a link, I believe) to their PM policies when you go to send a PM. In my mind, that makes Prosper's position on this even stronger.
Not that it matters anyway. When Prosper banned me, I sent a lengthy explanation of exactly why my conduct violated none of Prosper's rules in effect at that time, and also demanded that Prosper rescind my ban or buy me out. And Prosper couldn't have cared less. It counts on the fact that most of us have so little (relatively speaking) invested, that it isn't worth our while to sue Prosper, even though we would have a very strong case. Of course, that calculation almost turned out to be wrong once, which would have taught Prosper a thing or two. But, Prosper "got lucky" with the SEC cease and desist, followed by the class action, coming at just the "right" time.
