A few folks have asked me for the source code to the editor.
Up till now, I haven't made the source available because this started off as a quick and dirty hack, and the code is really ugly and disorganized. I've been meaning to clean this up before making the source available.
Unfortunately, it doesn't look like I'll have much time to do this going forward. So I'm just going to release the source in its present form.
You can now get the source from github at:
https://github.com/gluggy/Java-Mobi-Metadata-Editor