Q: If I decide to replace a file on my iTunes library with a file of the same name (assuming I decide to re-rip a song to a higher bit rate, for instance), will my iPod “know” the file is to be replaced next time I sync? If not, how can I “force” a file to be overwritten on my iPod?
A: This largely depends upon how you go about replacing the track. Normally, if you simply replace the underlying file within your music folder, iTunes will not pick up that anything has actually changed, and therefore will not update this track to your iPod.
If, on the other hand, you actually remove the existing file and then re-add the new one, iTunes will of course see this new file as completely different, in which case it basically removes the old one and transfers the new one.
The disadvantage to this method, however, is that the new file is effectively a completely new library entry, so any ratings, play counts, and playlist entries will be lost by doing this.
If you simply want to replace the underlying file, however, there is a workaround that should work: Simply edit the file properties after replacing the underlying file itself (by selecting the file(s) in iTunes and choosing File, Get Info) and make a change to the properties such as artist or album name. This will force those tracks to be re-transferred to the iPod during the next sync. This can simply be a minor change just to force the sync, and you can always change this back to its original setting later.
Note that this will be different if you are re-ripping tracks from a CD through iTunes itself—in this case, provided the saved CD track information (or CDDB lookup information) is the same as that assigned to the existing tracks, iTunes will prompt you as to whether you want to replace your existing tracks or not. Selecting “Yes” will re-rip the tracks based on your new settings and simply overwrite your existing library tracks.