I have been told multiple times that this is not possible, and by multiple people, even on insisting that I had heard others had been able to do so, and on insisting that the reason I had two orders in the first place was because that was how their site was set up for the online "upgrades." From your experience, it must possible, but clearly the systems and processes to do so are not trained or understood very well across the organization.
I am still hoping they refund my GGT deposit. I was told it was too late because I was in production (though nobody called me at pre-VIN time nor at in-production stage) but that they should be able to make an exception - but don't be alarmed by the automated email that would tell me I was too late. Supposedly it will take a few days to process. It hasn't yet.