They should change automatically. They are displayed on the screen as CHR$(32) spaces, so just copying from IE and pasting will be enough. Maybe other browsers are different, but IE displays them as spaces. This, I think, may have something to do with why the cannot be copied _from_ the post-a-message form's text box.
I will type 5 ALT+0160s here: ' '
I will now copy them from where I just typed them, and paste them here: ' '.
See? They copied as normal spaces. But if I were to copy from Notepad, they would be CHR$(160)s.