I think you probably can do it that way. But keep in mind that Asia Miles won't handle the booking. Consequently (since it's the booking that drives everything else, not the availability of upgrade inventory) it seems more efficient to have telephone sales check on the availability. In effect, that consolidates your steps 1 and 2.

You will still have to then call Asia Miles to redeem the upgrade, and have the ticket re-issued. To avoid getting trapped with an issued ticket, then finding that the upgrade inventory has disappeared in the interval between the two phone calls, you may want to do what I do: book, defer ticketing until Asia Miles has held the upgrade space, then ticket, then confirm and re-ticket with Asia Miles.

As I say -- YMMV................