There was no canceling the reward, as it was the same confirmation number that i got in April. Besides, had I canceled it I would've lost the reservation altogether, and I would've only gotten back 10k instead of 2x 10k.
I contacted spg, and the rep saw the issue, and said she would return the points, and would transfer me to the web guys to look into the issue of modifying a reservation to cash & points, and then it not working. Well, while I was transferred, I noticed that she never did what she promised and I never got my points.
Anyways, I spoke to this web guy/platinum concierge, and he was completely in the DARK that we are able to modify reservations. He told me, that "we usually cancel the old reservation and then book a new reservation". I then enlightened him that we can indeed modify reservations, and he begged me to please forward him the spg email that i got announcing this new feature, and was quite surprised. He also issued 10k points back into my account. I have no complaints to spg as to why I got points pulled twice for the same reservation (once in April, and once in June), as this was a new pilot program. But I would think that all spg employees (specifically the web guys) should be privy to any news that we are all privy too (you should have heard how many times he thanked me for telling him!)