2 questions for changes during the XONEX fares:
if I change the routing and the new route has more legs/more taxes/surcharges, I guess I have to pay for it? (if not I'd just book the shortest possible XONEX and then add legs after the purchase, so my guess is you do have to pay)
and assuming I do have to pay, do I pay at the original exchange rate at the date of the ticket purchase or the actual FX rate at the date of the change?

thx in advance,