This is something that's really bothering me: time travel is not possible, except as fiction. So the only "rules" of time travel are whatever the writers want them to be. Please give me a link so I can read Damon and Carlton's "Rules of Time Travel" - the only thing we know for sure is that whatever the rules are, Desmond is immune. Daniel said "whatever happened, happened" and the thing about being on the wrong track of a record. I don't think those are enough for us to say with certainty that the Losties can or can't do something or "they're going to break the rules."