MW50 merely allowed higher boost pressures and the max time to run that higher boost was 10 minutes after which you needed a 5 minute break.
That restriction is totally separate from any other limitations on running the engine at takeoff/miltary power at low airspeed. If the engine had a separate restriction on for example time at takeoff power that still applied over and above the 10 minute WEP restriction.
Running MW50 did not magically give the engine the ability to disregard its normal restrictions its cooling properties were a side effect and minimal. People seem to think if MW50 was permitted for 10 minutes then the engine should last 10 minutes regardless of how you mistreat it. That is just silly.
Gratuitous MW50 operation instructions in German :
