In earlier versions of Heroes 3, the "Neutral" and "Evil campaigns has unique background music, but it seems like they've been replaced by the "Good" campaign theme in the more recent versions.

Is there any way to fix it so that the "Neutral" theme (http://www.youtube.com/watch?v=pgDldwLtHvE) plays in the campaign screen for "Spoils of War", and the "Evil" theme (http://www.youtube.com/watch?v=Uu1pw1IcuYI) plays in "Dungeons and Devils" and "Long Live the King", the way it was in the earlier versions of H3?

It is impossible to fix something which is not required to be fixed.
0. Uninstall Heroes III Complete.
1. Install Heroes III RoE v1.0 from original CD (released February 16, 1999).
2. Play and enjoy. Moreover high quality campaign videos are only available in original RoE.