You can do it with the pot alone, no switch needed. Put one value cap on one end and different value cap on the other end of the pot. The wiper taps into the circuitry. Double the value of the pot you use like from 250K to 500K.

With the knob in the middle, it involves no caps. Rotated one way brings in the cap and rotated the other way brings in the other cap.

Simple hey?