A yes or no answer requires a little more detail. If your motor has a cable operated foot pedal system (not electronic) the answer is probably yes -- but with a qualifier. If your motor is electronically controlled (electric cable between foot pedal and motor) then the answer is also yes -- but with a more serious qualifier. If your motor is older and uses speed coils for speed control you can definitely add a reversing switch. But chances are it would already have one.
Any electronics in any device are polarity sensitive so the more modern a motor is, the likelyhood it has more electronics is high. Since you can't just reverse the polarity and still have motor control you must get past the electronics and get directly to the motor itself. I have not been inside every troller on the planet and you have not told us what you have so everything you read from here on is quesswork. But, if you remove the cover at the top of your troller shaft you should see two large gauge wires (red & black perhaps). Those are the high current conductors (the feeder) going directly to the motor. The speed control (electronics) would be the device those wires connect to at the top of the shaft and that device sends pulse wide modulated (PWM) signal to the motor. So a reversing switch would need to be inserted in those two wires going to the motor..
If the PWM circuitry is located in the actual motor housing at the bottom of the shaft, then the same technique applies but the wires to be attached to a reversing switch would need to be interrupted at the bottom of the shaft and routed upward to the switch. Much more work and perhaps not enough room in the shaft to do that. Outside the shaft is not an option.
Whatever switch you use would need to be rated for the maximum current draw of your motor or heavy current relays could be used with a lesser rated switch. I have a reversing switch diagram somewhere but will need to locate it. Stay tuned.