Why oh why do people always mess about with proper engineering?
The only reason to modify the thermostat bypass would be to (modestly) increase the cooling capacity. You will get poor heater response, slow warm up, increased fuel consumption, and will fail emissions testing if the engine won't stay at operating temp. You WILL NOT get any performance gain, and will in fact tend to overcool the engine most of the time.
The only application I would suggest for modification would be racing, in which case fan cycling isn't an issue.
Leave it alone and let it work. The fan only needs to run when the coolant gets to 100C -- temp won't change that fast to be a problem. Besides, you won't notice the loss of the four or five horsepower the fan uses.
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!