[MENTION=436365]CAPO[/MENTION]nus

-true, can only add a bound by calling in
-false, adding the new flight will reprice the entire ticket at current rates
-true, can add up to a year later
-true, no fee
-true, can be Y or PY
-true...

However, depending on your current fare you may need to pay change fees. Also, you have AMS-YYZ. It may price if you book a flight now from YYZ to say CDG or TYO. but if you try and add something that makes no sense like BKK to TPE which has no connection with the first flight it may not price.

Another big issue is that priority rewards do expire so if you book it and then decide to change the flight again after expiry you won't be able to use it. Hope that helps.