My advice? Wait until the April schedule is finalized in February or so, because you don't want to have called-in favors be worthless on yet another schedule change. If you wait until Feb, then you only have to deal with the rebooking hassle once.

I highly doubt that UA is going to endorse your ticket unless you bought the entire package as a single ticket, in which case the issuing party has the responsibility to transport you to your final destination. Split the ticket and you're toast (price you pay for cheap tickets).

Also, skip the JFK-IAD leg on the J41. Don't even consider it.