Originally Posted by
RangerNS
OP, you might be able to convert miles to nearly cash, buy buying a gift card.
But the biggest denomination seems to be $1000, and there are strange limitations (based somewhat on your luck of agent) on how many distinct forms of payments may be used per ticket. Or transaction. Or something else
They are generally considered poor value for miles. Your $1600 upgrade (assuming you could pay for it with 3 gift cards of $1000, $500, $100, which per above you can't) would cost 160,000aeropesos, enough to get you from Canada to eastern Europe in "first" class.
As for "why dont they let you"? Because they don't.
For ticket changes it's always always always 1 FOP with AC.
Unless you pay the change fee with one FOP, and the ADCOL on another (since they are two distinct transactions). But since OP talks about Y -> PY, we know there's no change fee. So a bit SOL as far as splitting goes...