How much does it cost to change a round-trip, restricted economy, international flight ticket?

If you have to change the ticket, you'll be responsible for the change fee and all applicable fare differences on the new ticket. The change fee itself depends on the fare rule of the ticket, and the fare difference will depend on how much you paid originally versus how much the new ticket will cost. No one here will be able to tell you exactly how much all of that will be -- you'll have to contact American directly to find out how much they will charge. Typically, though, change fees on heavily restricted international tickets on AA begin at US$250, so you're likely to be paying at least that much even before you get to the fare differences.