I think it's more likely that if it was a last minute substitution, it came up when Pistorius was on the stand. And if (IF! Pure conjecture here) there was a point at which he thought 'there's no way it could have happened this way...' it was possibly to do with the order of bullets.
Pistorius said that it was very quick, rapid fire, and it started and ended before he even knew it. The gun virtually went off on its own in his hand.
Dixon says yes - the order of the bullets were such that it was a sudden fall, and the head wound happened while she was still falling. It was that fast.
The witnesses, and the prosecution say no - it was a single, then a three. Bang. Bang-bang-bang. There was thinking, hearing and screaming time between the gunshots. There might even have been a change in aim.
This was the point which Roux spent the most time on during his initial examining of Dixon. How did the bullets happen - what was the timing, how did she start off (reaching for the doorhandle) and not facing straight and possibly talking to Pistorius.
This is utterly critical to Pistorius' argument of him not intending to kill anyone. The gun went off. It wasn't intended.
The food thing - it's not irrelevant, but all the experts have said that it's not an exact science, and even the prosecution one says you can only hope to get it accurate to within an hour either way, and it depends on metabolism. So no massive crime to disagree there.
I'm not intending to backlash you (and I really hope it doesn't read that way)! You're completely entitled to your opinion, and it was rationally and politely expressed! I just think it's a bit far-fetched that a crack pathologist would be worried out of the witness box. It's his job. I would imagine he's disagreed with opposition pathologists when he genuinely has disagreed with him -he's done thousands of autopsies, apparently, and they can't all be perfectly straightforward. Apart from anything else, it would be wholly unprofessional to say he totally agreed with something if he didn't, and that would look much worse for him.
He undoubtedly knew who Pistorius was when he asked him to come and work for him (and if he didn't, he could surely have googled). I think the even if the television was a surprise, the media interest wouldn't be.