An performance ECM tuner company Hypertech produced a "power stat". Theory was: Cooler tstat equals cooler engine, equals cooler intake air temps, equals denser intake air combined with enriching A/F mixtures and increased timing advance made more horsepower. I don't know if your out to lower coolant temps or make more power but with an non tunable ECM it might do more harm than good.
Not a good idea to lower engine operating temperature. There is no choke on a fuel injected engine --- the ECM looks at engine temperature by means of the signal sent by the temp sensor and compensates for lack of vaporization (cold engine) by lengthening the pulse width of the fuel injectors.
The net result provides an abnormally rich fuel mixture just as a choke would. As the engine temp increases and vaporization improves the pulse width is decreased gradually until the engine reaches full operating temp. Lowering the peak operating temperature would create an overly rich fuel mixture all of the time and fuel economy would suffer. Another possibility would be that a portion of the excess fuel in the cylinders could get by the rings and end up in the crankcase, contaminating your oil with gasoline.
I wanted to change/test a gl1800 thermostat to verify that if travels full open, but when I saw where it was located I did not attempt. Just how many shop hours are allowed for an experienced mechanic to change one out? What kind of can of worms would a home mechanic get into?