It's not difficult, but you need to proceed carefully because you don't want to cut a notch any larger than necessary.
I use a Dremel tool with a grinding wheel. The notch is about 1/8" wide and about 1/16" deep - but go slowly and make it smaller, than needed and then enlarge it until the clip fits. The clip tapers slightly, and you want to match the width near the finial. To test the fit, hold the finial end upside down .
I haven't had any of the 'snap caps' fail under normal conditions, but once the pen has been assembled, its difficult to take it apart without destroying the snap cap. CSUSA sent me a few extras to replace some that had been damaged. That said, I still don't like the snap cap design. In addition to the reliability issue, the nib dries out more quickly with a snap cap.
One hint - if you have a set of metric taps, try threading the snap cap before assembling the pen. The instructions call for using the stud under the finial to cut the threads as the snap cap is being installed in the cap - my experience is that threading the snap cap before trying to assemble the upper portion of the pen is a lot easier.
In addition to the dreaded snap cap, the Artisan FP has an ugly metal end on the body. I have a couple of closed-end version that I have been using on a daily basis that I like better. It does write nicely.
A final observation is that the section can come apart, and over time you may find that the nib portion will unscrew from the plastic portion. This problem is not visually obvious, and the symptom is that converters will no longer seat properly. The solution is simple - just tighten the nib portion of the section into the plastic portion.