Replacing switches and outlets
The copper cap holding the bare copper wires together is a crimp connector. You can cut this off and you will be left with the two twisted wires behind it.

Add a pigtail (a short piece of bare wire), carefully twisting one end of it around the remaining bare wires. Then put a wirenut over the bundle. Carefully bend the other end of the pigtail forward to wrap around the screw terminal of the switch.