I'm still not quite clear why they can't offer already-booked passengers the choice though - on the basis "when we agreed this booking with you, we thought the connection would most likely be ok (though of course never certain); now we think the risk is bigger than we thought. Do you want to keep the booking or change to something else?" Maybe just too complicated for the booking system, I suppose.
I go through this quite often when I book as early as when the new schedules come out. At this time my flight at xmas has been involuntary changed or canceled 4 times since I booked last May.
Each time I discovered this by surfing periodically into their web site and saw my reservation has been flagged as changed
(not a problem as they would have eventually notified me days before the flight)
Each time I researched their schedules for something better (same day, different routings to same destinations) so when I called them I was prepared to
suggest a better alternative for me.
Of course I try to avoid getting a refusal on their part by asking for something way beyond what I paid for in the first reservation.
If you want something than politely ask for it now that they owe you a return favor and have to re-do your reservation process anyhow.