I happen to have an old scratched up fender in my possession and I decided to do a trim job for a different look for the bike. Just cutting the fender straight looked too chunky to me up front, so I did a gentle radius just to break it up.
I started the cut about in the middle of of the fork tube indentations. Very low angle then did the radius, came back toward the outside edge to capture some of the stock flared part then around the front and off with the nose.
The tricky part is matching both sides. What I did was use some thin masking tape (pin striping tape would be nice) to mark it before the cut. That way you can experiment with different styles before the cut. Just hold the fender out there, squint and imagine everything below the tape is gone.......
I used a Mototool with a fiber cut off wheel. That is some thick plastic back toward the center of the fender! Try to keep the cutting wheel at a 90 degree angle as you cut and you'll have less filing and sanding to do. The speed of the Mototool and the speed of how you cut is another delicate balance. It seems to work better to make multiple cuts instead of trying to power through it one time. It's a fine line between cutting and melting/welding. Keep an eye on the cutting wheel mounting screw, you don't want that gouging the good side of the cut.
The tip or front of the fender is tough because you are going from the side radius into the rounded nose. Try to make it as gentle as possible so it looks, well like it's supposed to look on a fender.
Make sure you wear some eye protection. I wasn't at first because I was cutting down low and the plastic was hitting me in the stomach. But I adjusted it up for this one trim and a piece of melted plastic got me right in the inside corner of the eye, more tear duct area. That was hot!
I think it turned out ok. I wonder if I should have "cut it" a little longer? Have a little room for a Suzuke "S" on the front. It's weird not seeing the fender out in front while riding.