Is it possible?

[alarioninglorion]

play rsii with a sub music mod. The music is really wonderfull, but after playing several hours you just want some variety; maybe if there were more "themes".

[Angry_roman]

Easy C:\Program Files\Steam\steamapps\common\rome total war gold\data\sounds\music.

or wherever your rtw is installed. Replace the music files with the ones you want. You will probably have to listen to the music in there and find witch one plays at the the time that you wanna change the song.