If you book a flight using Mileage Upgrade Award aka miles to upgrade an Economy ticket to Business class and/or Polaris, can it be revoked for any reason? I was all set to book a trip RDU-SIN in Economy but partner would prefer Business class. I haven't done this for quite a while and wanted to make sure that rules haven't changed. I don't want to book an upgrade award then have the rug pulled out from under my feet.