Not sure to be honest.
Posting the question three times on this forum probably won't help! (just kidding)
I agree that once you've been allocated a build slot it is impossible to change. Your only hope may be that the garage have somebody else who would prefer a pre-facelift model, or someone who cannot wait 8-10 weeks to get hold of the car, who they can offload it to.
Failing that, you can cancel the order but more than likely lose your deposit and then place a fresh order.
Not sure arguing that the dealer never told you a facelift was coming despite it being all over the internet is the way to go. They'll just say that if you read it on the internet that you should have known it was coming. Best to leave that part out of the discussions.