Quote from TykerDoesn't that then also override the file for any maps played afterwards until the game is restarted? I remember that being a problem when I made maps for TF2. Is that still an issue now?
As far as I know, any packed files are only run for that specific map. When you make custom soundscapes you also have to pack your custom soundscape_manifest.txt, thus overiding (temporarily while the specific map is being ran) the local soundscape_manifest.txt for the user.
I would assume the same applies to the voice files.