If they actually output 100 watts (assuming the amount of current won't be limited), you are drawing more current through the wires than a 55 W bulb by a factor of almost 2. Power (Watts) = voltage x current. Your voltage is limited by the alternator output, roughly 14 Volts. The only way to get 100 W is to raise the current/reduce resistance. Power also = Current squared x Resistance. Assuming the higher current doesn't exceed the design rating for the wiring and doesn't blow a fuse, your next problem will be gradual melting of the housing which was designed to dissipate half as much heat. Some using 100 W bulbs have found damage after a few months to years of use. Probably cheaper to get the right size bulbs than a full headlight assembly replacement. I also wouldn't want to pay parts and labor for replacing the wiring harness. Your call, and your piece of mind.