This was the first time I have ever worked with this finding and I have a few observations. First off, this is a strong, good quality metal. Once it has been crimped, there is no going back. This was actually the second set I had worked with. The first set, I did not get a tight enough crimp on the cord and it came right out. I tried to re-open it to re-insert the cord into the end crimp but it would not work. I tried again (with another set of crimps) with the nylon jaw pliers and while it did not leave a mark on the metal, they are much more difficult to use. The nylon jaw is completely smooth and it is pretty difficult to get the angle right. One time, the crimp slipped out of the pliers and flew across the room, resulting in my finger getting clamped instead! OUCH!
Update: The below image demonstrates the tutorial above using the nylon jaw pliers. As you can see there is minimal scuffing, but they are in much better shape than the ones pictured above. (The one on the left is the one that went flying and made me pinch my finger. Thats probably why it has a little more damage than the one on the right.)