You could try KingSparta's "Replace Master" plugin:
http://www.spartasoftware.com/MC-Plugins/11/index.htmlhttp://yabb.jriver.com/interact/index.php?topic=35393.0I have not tested if it can write the "Number Plays" field, but I suppose so.
Another option would be to use Mp3tag for copying the field info:
1. Change MC's "Number Plays" library field so that it writes to the file tags.
2. Play a test file with MC so that the play count info gets written to the file tags.
3. Configure Mp3tag to write ID3v2.3 ISO-8859-1 format tags.
4. Open the test file in Mp3tag. The extented tag info window in Mp3tag will show the "Number Plays" tag as "COMMENT MEDIA JUKEBOX: NUMBER PLAYS". Change the tag value once and save the change (in Mp3tag). After this Mp3tag can write this tag correctly to other mp3 files.
5. Use Mp3tag's tools for mass copying the info to this tag.
6. Inside MC do: Update Library (from tags)
7. Remember to change the library field back. Otherwise MC would change your file tags after each play.
8. Also, you should do "Update Tags (from library)" after changing the field back. This removes the Number Plays tag from the files. - This works with mp3 only. With other file formats you need to do: 1. Remove Tags, 2. Update Tags (from library) or use Mp3tag.
EDIT
You should use the latest Mp3tag beta build from here:
http://www.anytag.de/forums/index.php?showtopic=57.
For the step 5. you can use Mp3tag's "Actions" (Convert > Actions).