I was also able to get an existing reservation at the St Regis Bali adjusted without having to cancel and pre-book. The hotel was not sold out however my original reservation remains intact and points refund has hit my account. That was through the US SPG platinum phone line.
Did you have to call several times or were you able to get an agent that had a clue right away? Also, was this in the last couple days? Thanks for the update.