
Upon launching the game after getting this error, it seems to be vanilla XW:A. Nothing has actually updated.
For my Steam version, I copied the game to a new location and started renaming the files to be replaced (makes it easier to undo). Some were replaced by new files, others were not. But this started getting tricky when the files I needed to rename were the ones used to detect if there was an actual copy of XW:A at the file location. I had to hold off on renaming until after the verification. But it kept finding more and more things it couldn't access. I'm up to the MISSIONS folder now. This version now refuses to launch at all.
I've tried snoozing my antivirus, tried resetting attributes, tried the security tag permissions, tried running as admin... there has to be a better solution than running the installer eleventy billion times and renaming everything it whines about on a case by case basis and hoping I'm not renaming anything that isn't fully replaced by the patch.