Too much heat can damage the insert and the paint. That being said, it generally does not take much heat to remove a putter shaft since most have a shorter bore depth. There are a couple of things you can do. You can use club shield (GW1039) and spread it on the face insert and on the paint around the hosel bore. It will provide some level of protection, but the longer it will dissipate the longer the heat is applied. You can wrap the head in a cold, damp cloth or rag. This can help keep those area cool long enough to get the shaft to break loose. No problem in doing both of these at the same time. Also, heat from the back side of the shaft do not keep the heat on the shaft for more than 10 seconds with a torch and approx. 25-30 seconds with a heat gun. As long as you keep the head wet and cool, the shaft should come out without any damage to the head.