The general rule is that if the originally purchased itinerary is International, then that ticket can be exchanged without penalty for ANY higher fare ticket. Almost all domestic restricted fares carry a $100 fee to re-issue, even if you are just buying up to a higher fare bucket with no itinerary changes.

Undocumented feature: You can exchange a non-refundable international ticket for a wholly-domestic itinerary without paying a change fee, as long as the domestic ticket costs more than the international one.