I’ve been able to book an international flight and domestic flight (both economy) on a special Amex Plantinum Travel Desk AA fare that waves the change fees. The costs for both the same as if I had booked it directly through AA.com.
In in the case of the international ticket I changed the return flight 3 times right up until the last minute and incurred no change fee or fare increase (may have been just lucky with the fare increase).
Not all flights appear to be available - but I always check with Amex first before I book directly with AA now. Given AA is also my selected airline for the Business Platinum I also get the 35% points rebate when booking with MR points.
Pretty amazing perk of the Platinum card, in my opinion.
Do you happen to remember if the booking class was the same on both fares?