I have found a simple trick to aid when replacing tubing on the NM2, 3 and 4's. I use a heat gun to turn the opaque tubing clear. It is best if you have a small diameter welding nozzle on the gun. The tubing is more flexible after treatment. This avoids the problem of having multiple lines breaking as I am attempting to change them one by one. I have found this helpful. I hope you do as well. Only heat the tubes till they are clear, any further runs the risk of melting the tube. Also care must be taken when the line runs past wires or electronics. Any residue displaced should be vented during post replacement testing.
All the best, Ron.