You know, thinking about it, I think one thing about fanfic that makes it, hmm, less pressure than original fic in this kind of situation is that the possibility, at least, *does* exist of doing both. In practice, writing two fanfics that are very similar except for one plot point is something a person probably wouldn't do often, if at all ... but the possibility is there, you know? Writing it one way doesn't mean that canon is locked into that one thing being true forevermore. And even if it affects this one story, it doesn't affect your other stories. Whereas in original fic, once you've made that decision, it's going to influence how you write the characters from now on -- it has to. That particular set of characters are locked into exploring the ramifications of whatever plot decision you've made. It's an intriguing difference that I hadn't really thought about much.