Thanks cyborg - I didn't see the options on the manage my booking section of the SQ website so decided to try my luck with an agent.

I just finished speaking to an agent using the SQ chat function and they confirmed that I would be eligible for a one time change (+/- 7 days from original scheduled departure date) or a full refund of the miles to my account and fees and taxes to the original mode of payment. The agent initially tried steering me to accept the changes as the only change would be an earlier arrival time but after I asked what my other options were (given this was a formal schedule change that I received an email notification about that directed me to call customer service if I wanted to discuss alternate options) he confirmed I was entitled to exercise a one off date change or cancellation and refund (which again would otherwise not be allowed for this type of award booking).