I believe he means to always file on the sight and not on the barrel to make the sight fit. I have heard that the sights can be a little tight and require a little fitting to make them fit. I will be in the same situation as you as I am picking up my gp100 soon and one of the first things to do will be to find a front sight that will be easy to see for my aging eyes.
I too wanted a new front sight for my gp. I opened my tackle box and found the brightest piece of plastic on my lures and cut it to precisely fit the ramp on my sight. Glued it in place and it looks great. (I'm quite particular) You might want to give it a try before buying one. It looks much better than a painted one IMHO.