(1) If a person owns a motor vehicle which has interchangeable bodies for same so that at one time the motor vehicle may be classed as a passenger automobile and at another time as a truck, has registered same as a passenger automobile, he shall, before using it as a truck, pay the registration fee required for trucks in KRS 186.050. In such case the owner shall be allowed credit for the unearned portion of the passenger registration fee on the truck registration fee.
(2) A passenger automobile shall be construed to have been converted into a truck when the change is such as to enable same to be used as a commercial vehicle.