Can 2 circuits exist and work independantly in an electric guitar
Sure. You just need a bypass switch. You would probably want to disconnect the pickup from the input to the preamp as well, as electric guitar pickups are sensitive to loading. That isn't hard to achieve though:







simulate this circuit &ndash; Schematic created using CircuitLab

(Rather simplified "preamp" with no gain, DC blocking caps or other components shown - just the 1M resistor which sets the input impedance, and is disconnected with the preamp switched out.)