Well, I learned something from your question. Here is the Help entry:

"Convert Media, a Premium feature, allows you to change the format and quality level of the media files associated with your media clips. You can convert audio media from any supported format (except secure formats) into MP3, RealAudio, and Wave formats."

I have not bought the Premium upgrade, but I see that it does permit a user to change the clip info on an existing MP3 file, as well as when converting from another format.

So there we have it. All I need to do is upgrade. Off to the bank!

Thanks
HD