If you were originally on a mixed award, UA's system will default to keeping you in the same fare classes you were in originally. If there's saver space on the UA flight, I doubt you'd have much trouble getting it; if not, I'm not surprised they'd insist on economy. It's an edge case, and I'm not necessarily saying that they're right, just that I can see their side and can't really prove that they're wrong.

Not being able to change a connection point doesn't make a ton of sense. I get the sense that agents have been instructed to be more strict after schedule changes, but they haven't told us exactly what they're being strict about (and different agents seem to have different interpretations). I've read some reports that agents have claimed that you can't change carriers after a schedule change, but this is the first time I've heard anyone claim that you can't change connecting airports.

It seems like you got an acceptable compromise, but you can still work to improve it if you want. Keep an eye on inventory for the day you actually want to travel; if some new inventory opens up there, you should be able to snag it.

Good luck!.