Yes, that'll work fine.
The only caveat is that the artist, title, and length (in seconds) of the MP3 in the media library won't be updated when you do this, but that's currently only used for display purposes so it doesn't matter to Centova Cast. Centova Cast v3 will eventually use the track length for scheduling purposes, but v3 also automatically detects and reindexes any files you upload via FTP, so it won't have any impact there either.