No. Never cut the heating mat. The floor heating mat is designed with a very specific resistance in order to consistently maintain heating at the chosen wattage per square foot. Trimming the heating cable in the mat would lower the resistance of the cable causing the system to overheat. Adding heating cable to the system would raise the resistance and the system would not heat properly.
If you think you have the wrong heating element, contact our 24/7 Technical Support Team by calling 1-800-875-5285.