It won't be hard to single out the sim-neurons specific to a particular anatomical macroregion.

That's true, but ultimately the regions of the brain are not completely islands. The circuitry connecting them is itself intricate. You may, for instance, be able to extract the visual cortex and get it to do some computer vision for you, but I doubt extracting a prefontal cortex will be useful without all the subsystems it depends on. More importantly, how to wire up new configurations (maybe you want to have a double prefrontal cortex: twice the cognitive power!) strikes me as a fundamentally difficulty problem. At that point you probably need to have some legitimate high level understanding of the components and their connective behaviors to succeed. To contrast, a vanilla emulation where you aren't modifying the architecture or performing virtual surgery requires no such high level understanding.