I have already modified several Opinel knives and will take you step by step through the process today. I’ve tried a few different methods. The French folding knives are available with carbon steel or stainless steel and they are quite cheap.
First I take off the ring that locks the blade open and closed. Then I work on the beech wood handles with rasps, files and sandpaper. By the way, if you are wondering about this strange sand paper saw: I have the idea of Dave Canterbury, who has a great video about it.
As soon as the handles are finished I disassemble the folding knives. Often the pens have to be filed off a bit. With used knives, the pins are often a little bent and difficult to remove and replace. I had to replace one pin completely, I used a steel nail.