Fronts, not really. Rears....... Honestly probably not that difficult but I went a little to far on the drivers side and ended up with a small hole. Hard to explain. If I did it again I would do small little slits and then bend them in.
Hard to explain but have your cut line terminate were the point of your rear bumper is (were the bumper meets the body) You do that and you are golden. On thing is that it is not like a regular fender, there are two different pieces of metal, one for the body and one for the tub of the fender so you will have to seal it some how. Some people used body panel adhesive, I used silicone, but I think doing the slit cuts and bending the metal up would be the best way. Then seal the metal with silicone and paint.