Actually this post belongs in the Tech Support Vanity section....assuming you have paid for a subscription and don’t mind waiting on hold with the Freeper Tech in Calcutta.
If you’re a windows user, the best program in my experience has been mediamonkey
great series of articles at lifehacker.com
Any program you can use to set it, a user can use to clear it.
What I use on Linux is a program called EasyTAG. It’s a powerful, free tool for setting tags on a variety of file types. I believe they have a windows version as well.
http://easytag.sourceforge.net/
You can try MP3 Producer (shareware, not free) from this link http://www.mp3developments.com/mp3producer.php or elsewhere.
Failing that, you can ask someone to create a simple Visual Basic or elementary C++ program that can either handle batch operations parameters (e.g. my*.mp3) itself or can be used in batch mode with a single file parameter, to find and set/reset the Copyright bit in ID3 tag info, possibly using this structure and calls - http://docjar.com/docs/api/joeshmoe/mpeg/MPEGInfo.html.
Hope it helps.