i believe this is the same as my "piddle valve"
what that does is allow the rest of the cooling system to warm up a bit to avoid the thermo shock of 160 deg water suddenly going through the 1st part of the system especially in winter
It also helps to release air pockets trapped under the thermostat
I've always drilled at least 2 holes 1/8" in the "plug" portion
another thought
160 thermostats crack open at about 125 deg an are fully open at 160
these things are motivated by a wax pellet that expands and contracts
and drilling there might keep the pellet cool and the thermostat closed untill it is really at 160 perhaps warming the engine and oil a little faster