Heat range has essentially zero to do with "cooling" an engine...has to do with keeping the tip of the plug at the correct temp to keep it clean by reducing build up or causing premature detonation if too hot. An increase or decrease of the tip area will not do a thing for cylinder temps. How would anyone believe that tiny tip will reduce the temps of the thermal mass of the Iron liner, piston and valves/ head?
"Heat from the combustion chamber escapes through the exhaust gases, the side walls of the cylinder and the spark plug itself. The heat range of a spark plug has only a minute effect on combustion chamber and overall engine temperature. A cold plug will not materially cool down an engine's running temperature. (Too hot of a plug may, however, indirectly lead to a runaway pre-ignition condition that can increase engine temperature.) Rather, the main effect of a "hot" or "cold" plug is to affect the temperature of the tip of the spark plug." gsparkplug.com
I remember people saying in the '60's and '70's the same silly thing....."if you car is running hot put colder plugs in"! LOL...... kind of like dropping an ice cube in a 5 gallon bucket of boiling water.........