Yes, you would drop some of the voltage presently running the motor, across the resistor, slowing the motor speed.
BE CAREFUL of the value and wattage of the resistor. I don't know what voltage your motor is running at, or the current to drive it. Too much current through the resistor, and if the wattage isn't right, you'll burn up the resistor. Wrong value of resistor, and you might starve the motor for the current necessary to drive it, causing it to overheat.
When you do this, just leave the compartment open, and touch the resistor and motor once in a while, to make sure something doesn't rapidly overheat, if you guessed wrong.
Of course, you COULD give us the information off the motor faceplate, Voltage, amperage, anything else useful. And then one of us can tell you more accurately what
resistor value and wattage to use.
