Welcome to FlyerTalk!
Originally Posted by
RichardJFuller
I am curious if United is 100% in the right here, or if it is reasonable for me to have expected more from them given the situation?
Yes and yes.
Your contract officially is from BOS to ***; the routing is not guaranteed. In that sense UA is within its rights to make that swap.
You're also within your rights to ask for a refund if the revised itinerary is not to your satisfaction. Which you did.