For me to wake up as Britney Spears, would mean the atoms in her brain were rearranged to encode my memories and personality... If that isn't what we mean, then we are presumably referring to a counterfactual world in which every atom is in exactly the same location as in the actual world. That means it is the same world. To claim there is or could be any difference is equivalent to claiming the existence of p-zombies.

I know p-zombies are unpopular around here, so maybe by 'equivalent' you merely meant 'equivalently wacky', but it's worth noting that the view you rightly dismiss here is quite different (and arguably more radical) than Chalmersian property dualism. After all, phenomenal 'qualia' are still qualitative (descriptive) features of a world, whereas you're imagining someone who thinks that there can be differences in numerical identity even between qualitatively identical worlds. (In academic circles this view is called 'haecceitism'.)

Anyway, as a property dualist who shares your anti-haecceitism, I just found it a bit strange to see you describe haecceitism as 'equivalent' to property dualism, and so wanted to clarify that the two views are actually quite independent.