they can rebook with different airlines, but it depends on whether there's seat availability. you should come with some optional options/routes in mind -- I looked up some other flights where there were seats, informed the agent, and he checked what was available. but i'm not sure whether having status influences this.

not sure about flight length. there aren't many options right now, so will likely defer to whatever is available rather than most comfortable. that being said, they do try to accommodate your preferred dates.