It is extremely easy, Do you have any experience using a dremel?
If not I would suggest you take your time and experiment on a few pieces of plastic similar the the fender. The key to doing it well is patience. I drew out my line of the cut on paper I taped to the fender. Using a flexible ruler make sure your lines are symmetrical. With the paper taped firmly in place I scored the plastic of the fender with a razor blade (you could probably just use a erasable ink pen) right where my line had been on the paper. That served as my cutting line. Make sure you give your self a bit of extra room so that you can sand around a 1/8th - 1/4th of an inch and get the nice rounded look you have on the stock fender.
Then move from around 80 grit to 120, 200, 400, 600. That would probably be good for most people but I heat treated the edge on mine and it gave it that nice plastic sheen the stock fender has.
You won't regret it, but make sure you have the time needed to finish the project, especially if you are new to custom work.
Good luck!
