Can I use high wattage bulbs (100/80) without making changes to the factory front lights wiring ?

 

I wouldn't risk it. The bulbs may be fine for like a month or two but the real damage will occur about 6 months down the road, and your wire harnesses will begin to burn out and will need to be replaced which can be pretty expensive. If you want high wattage bulbs, get a harness. If you want improved lighting and don't want the harness, try PIAA Superwhites.