In my opinion based on testing with my engine, this type of cooling modification is a waste of time and money.
I can't speak for others engines or applications, but in my turbo 6.2 I have digital gauges with RTD type coolant temp sensors in the factory location in the front of the driver side head, in the glow plug thermistor port in the rear of the driver side head, in the radiator inlet hose, and the radiator outlet hose. The front and rear of the driver side head are within 10 degrees at all engine operating conditions and usually within 5 degrees. The rear sensor is almost always cooler, indicating more flow is not needed at that location.
I've swapped the gauges and sender probes around between all locations and these results are consistent. In my engine, based on testing and data there is no reason to modify the cooling flow path specified by the engine designers and built into the cylinder block.