Well, it took a few days, but "the system" worked for me this time. AA sent a request over to LAN to change my connecting flight due to the schedule change, and LAN allocated the seats on the "rational" flight (which were not initially displayed on the AA system). Given my past experiences navigating the minefield that is booking LAN award travel on AA, I am happy to see this result without having to "fight" too hard for it.

That said, you still have to be "on your toes" when booking LAN on AA. Nobody will notify you of a schedule change, but if you check your itinerary on AA.com, it does seem to flag schedule changes. So you need to check this periodically and call for revisions when necessary. Also, don't trust the AA agent to correctly read LAN's schedule. Before calling, go to LAN.com for their actual schedule, and be prepared to give the correct flight numbers to the AA agent to request. As we all know, there are quirks in AA's display of LAN availability. In this case, LAN seems to be operating some flights coded as LAN and others as "LAN Express" (no difference as far as the consumer would know, I think it's a legal thing), and AA wasn't displaying the LAN Express flights.