Even if issued by a TA, if the ticket is 001 (ie AA plated), the AA round the world desk should/will handle date changes. And if purchased in the USA, why would you not book directly with AA?
Other airlines handle date changes without the US$125 re-issue charge per the Explorer rules, but do charge a "service fee". Eg I am paying AU$30 to QR for such privileges even though booked with my long-time TA. QF would likely charge rather more.
Just wandering
Fred