Question on exchanging a ticket
 

If I buy a business class (R) fare on the QR website IAD-SIN / BKK-IAD with a change fee of $530, can I pay the fare difference and use it anywhere on the QR network worldwide or just on the existing city pairs?

I called QR and got a rather confused agent who told me nearby cities or same continent which doesn't make too much sense. It would seem either exactly same routing or not.