I was able to book an Advantage award for an upcoming flight (SQ32/33) but am currently still waitlisted for a few Saver awards on the same flight. If by chance the Saver awards do clear, would I be able to request a refund on my Advantage award to book the Saver?
Yes, you would be able to switch to the saver and get the excess miles refunded to your KF account.
BUT ... I would imagine it being highly unlikely to happen: Why would SQ open up Saver waitlists when there are confirmed / ticketed Advantage awards booked?
(The scenario where you might have more chance of success is, you are ticketed Advantage on one flight, and waitlisted Saver on a different one)