Critically, the structure is spatiotemporally contiguous throughout these changes - which is totally unlike the transfer hypotheticals.
Ok, so we make the transformation slow enough that the brain remains spatiotemporally continguous - a phrase which should be used more often. For example, we could replace neurons a few at a time with silicon analogues of the same general physical characteristics (eg, density, flexibility, etc) and functional behavior.
Again, this is just asserting the conclusion that the physical structure of the brain is unimportant, and then reasoning backwards from that conclusion.
The physical structure isn't dependent on the composition of the molecules that make it up, aside from requiring just enough functionality (and maybe some timing tweaking here and there) so that the new structure works like the old one did.
I think what you're saying is akin to claiming that something without wheels, differentials or a steering column is still a "car" which "drives." It may be a highly efficient vehicle, but it's not going to "feel the same."
Unless you took great care to do so. I must admit that wood tires isn't really taking great care.
That's the point here - the mind isn't a homunculus inhabiting your head, which can simply get a new job managing a different theater.
What makes you think that? I think it is, it just is something we haven't figured out how to do yet. I see here the same abstraction division as we have in computer systems between hardware and software. The human mind is the software. If we make the hardware sufficiently compatible, it'll run on that just fine.
All evidence to date supports the materialist proposition that to radically alter the physical structure of the mind/brain would be to radically alter its subjective character as well.
Which, let us note, is just not that much in the way of evidence. And we're entering a era where far more aggressive technology changes can be made to the human brain.