The best way to cut a track is to cut through it in two places with a sharp knife and remove a copper section.
Caution!!! Use a good quality knife and don't press too hard to avoid breaking the blade.
Score many times instead of pressing hard. Keep your fingers out of the cutting path.

If the two cuts are close together, the copper will lift and you can scrape it off with the knife. Angle the knife towards the center when cutting each side to make it lift. Test the resistance between the two sides with a multi-meter to ensure there is no copper sliver connecting them if the cut width is very narrow.

If the cuts are further apart, heat the section with a soldering iron tip to make the copper detach from the fiberglass base. The section of copper can then be more easily removed. For StripBoard and ProtoBoard, cut at two adjacent holes and remove the 0.1” section between to make the cutting easier.

Pro-Tip: Color the cuts with a red marker to make them highly visible. This makes it easier to identify which track sections are no longer connected.