We all know that one can either leave all but the first international segment Open or actually date them and book a flight number.

But is it possible to combine the two - ie have some segments dated with flight number, but others open?

The reason I ask is that in planning my next xONEx, I am going to use a NA flight which I fear may disappear before the time it comes to fly it. If I leave it open and AA cancels the flight, I am left stranded, as the only way to get between the cities would be to go via a hub and that would put me over the NA segment limit. OTOH, if that segment on the ticket is dated with the flight number, and AA cancels the the route, i will be protected (won't I?) and they will have to reroute me.