Thought I'd just report my positive experience with AA's ATW desk yesterday
Last July I purchased from AA an ex-MPM DONE6, just before the price rise on August 1st
All the dates were dummy dates - all between June 8th and June 23rd.
So yesterday I phoned the ATW desk to change all the dates, except the first two (MPM-xDOH-BKK; to change them would have triggered a re-price at today's prices

)
The process was completely painless - eleven minutes from go to whoa.
Received an email confirmation of the changes 25 minutes later
And this morning MyFlights emailed me the changes, along with the new ticket numbers.
So this itinerary has now been re-ticketed a total of six times, the previous five were due to scheduling changes or flight # changes.