I'm assuming the TZ is a pick up
Normally tone controls are connected to the output of a pick up - the tone pot has a capacitor connected to it which then connects to ground - as you turn the tone pot more and more treble frequencies are shorted through the capacitor to ground - resulting in more and more bass - so the action of the tone pot is maximum treble at one end and maximum bass at the other.
Altering the size of the existing capacitor should give you more bass at one end, but the same amount of treble at the other - I would try a different capacitor first......................I think