So I contacted united and asked them. A change of airport is considered a change in routing: that's the NEW rule.
So changing the connection from NRT to HND is a change in routing and need a reissue. Here is the quoted response:
"A change in departure, connecting, or arrival airport is considered as a change of routing. Making a change in a reservation will incur a change fee and a potential fare difference depending on the routing and availability. Please feel welcome to reach out to us if you have further questions. ^JJ"