I think you need to definitely ask Richard – BUT – there is a strong possibility the bridge plate would need to be slightly larger, which would mean pulling and replacing that, which is a truly undesirable job, the bridge itself would probably have to be replaced with a larger one, less of a problem, but still a pain to do really cleanly, and the bracing and top would probably be OK, although they may prefer to have those slightly heavier as well, if they know it’s for a 12 string – But the biggest problem may be the headstock and neck width – you might be able to fit 12 strings in a 1-¾” nut space, 1-13/16 would be better, but I think mine are 1-7/8”, but I really doubt you could physically get 6 more tuners onto the existing headstock, so that would almost require a new neck – maybe they could scarf a new plate on, but I kinda doubt they’d want to handle it that way. All that adds up to a pretty difficult, costly, and time consuming project in my book.
I would say it’s worth keeping your eyes open for an in-stock guitar, or better, a used one – it seems that people buy 12 strings, after a while decide they don’t play them enough to warrant keeping them, so sell them at pretty reasonable prices – I mean, they are SCGC instruments, so you’re not likely to find them at a fire sale price, but when I’ve seen them, the prices seem far more reasonable than an equivalent 6 string guitar –
And selling any higher end guitar these days is a pain – you read the regular forums, and most of the players can’t hear a difference between a $600 Guitar Center special and a $15,000 hand made instrument, and many that can will question the worth of the difference. A beautiful guitar, like a Santa Cruz, and especially a lesser known model like the OM Grand, is gonna take a little longer, and require a bit more promotion to sell. I’m hoping that after Xmas, the market might warm a bit. But I have zero insight into selling – I just like buying – 😄