Yes, it'll have significant side effects. The default file encoding on Windows is your configured code page (1252, in your case), and there's no good way around that default. The easiest immediate fix is to re-encode that file yourself.

Perhaps what we could do instead is allow the first line of a .pth file to be a coding comment? Then site.py can reopen the file with the specified encoding.

(FWIW, when I added the ._pth file, I explicitly made it UTF-8. But it had no history at that time so it was safe to do so.)