In a traditional wiring the fixed resistance section of the pot goes to ground. The incoming voltage (signal) goes to the wiper and is dragged along the resistive element which varies the impedance. In a shunt configuration the signal goes through a fixed resistor (no moving parts) and the pot is rewired so the wiper varies the resistance to ground, out of the signal path.
To wire it as a shunt, you'll swap positions on the pot with the center wire (going to T1/5) and the ground. The ground is now on the center lug and the long wire on the right one. The short wire from the selector switch (on the left lug) is removed from the lug and you solder the resistor to the wire's end and attach the other end of the resistor to T1/5. The left pot lug is no longer used as the resistor replaces that function.
Good listening,
Lary
