You certainly can.
Check out the sticky threads on the official
Look & Feel forums for the full scoop.
The short version ... create a
everquest II/custom_music directory and put in there whatever you want to listen to. The hitch? You have to name it properly ...
For example, the music from Lavastorm drives me nuts. I want to replace it with my_awesomer_music.mp3
I have to track down the file that plays when I'm in lavastorm:
EverQuest II\Music\zones\lavastorm.mp3
I have to rename my_awesomer_music.mp3 and put it in:
EverQuest II\custom_music\zones\lavastorm.mp3
Hope this helps