I think if you don't have MW-50 on the plane, which might be the case for some servers, then you should keep the CB for MW-50 off.
From my experience, if you go to that power level where MW-50 would be injected, and don't have it, and after lets say a short time of 10-30 seconds, go back the plane will still fly for some time 10-20mins. Then the engine will die...
You could try to keep the CB for MW-50 and external tanks off. Then take off should be done with cowling fully opened. After takeoff you can close it slowly until you reach the 100°C coolant temp.