You need to parent onAdd AFTER you set file name:
function SCS_NewSounds()
{
BreakBrickSound.fileName = "./misc/blank.wav";
}
package Content_Dependencies {
function BrickBreakSound::onAdd(%this)
{
%this.fileName = "./misc/blank.wav";
parent::onAdd(%this);
}
};
activatePackage(Content_Dependencies);
If you parent it before, its just going to add the normal sound, then change the var, which doesnt change the sound.