There is the issue from the other thread about changes to the first flight. Then there is this issue, which is about changes to a flight that isn't the first, and isn't even the first international flight. This agent is saying that there is a new rule that prohibits changes to the first intercontinental flight.

As a separate, but related issue, there's the question of what happens if this flight is permitted to be changed. My TA is saying the ticket would need to be re-issued, which triggers a fee and maybe a re-price. But the OW rules, to me, say this is a free change.