Has anyone purchased an xONEx itinerary ticketed by AY, and have there been any problems?

One of my potential ex-ARN DONE4 itiineraries is substantially cheaper (per the online tool) if the first leg is on a AY codeshare, but I'm nervous about the ongoing "mantenance" of the ticket when the inevitable date changes, and potential itinerary changes, need to be made over the next few years.

[Perhaps I have misunderstood ---- am I correct that one always needs to go back to the ticketing airline to get date/carrier/itinerary changes made?]

Thanks in advance for your advise!