I have a bernina serger. I have never unthreaded it. When I change colors, I cut the threads from the spools, replace the spools and tie the different colors together. I then push the foot pedal and hold out the end threads until the knots come down to the needle then cut only the thread to go through the needle - works out perfectly everytime and my machine is many years old. My machine is also coded with colors for each spool of thread - would be easy to follow if I ever unthread. Good luck!