Can i modify my yamha fzs into fazer

That's absolutely useless dude. To modify the FZ-S into the Fazer, you need to add the Fazer dual headlight by removing the FZ-S headlight. First of all understand that manual addition of headlight won't as perfect as the factory. So there will some minute disturbance you will feel while riding. It will be uncomfortable for you. Moreover, it's way easier to ride with the FZ-S. Because, it's naked and made like a street bike. So, it will be much easier in turns. Meanwhile, a semi-faired machine decreases your confidence at high speed. Also chances are there to catch up with the wind.

So if you want looks go for modifications. Well, if you want a perfect ride, ride with the existing machine.