Re: Soldering handle hack
A 53-ohm temperature sensor is probably some kind of thermistor.. all resistors lose resistance as they get hotter, and some are calibrated to do it in a very predictable way.
A 3-ohm temperature sensor is probably a thermocouple.. two wires of different metal (copper and steel, kovar and platinum, etc) that generate current when they get hot.
Just telling us the resistances is about as useful as telling us the color of the handle. If you don't know what kind of sensors they are, dig around for documentation and find out. Also look for information about the temperature control circuits in the Lafayette and Hakko control boxes. Those will give you a better idea of whether it's even possible to exchange elements the way you want to.
When you void a product warranty, you give up your right to sue the manufacturer if something goes wrong and accept full responsibility for whatever happens next. And then you truly own the product.