You could just measure the value of the rotor angle, compare it with a constant block (you could just subtract the two and use the comparetozero block), and then if the output is true, add/subtract 10% where necessary.
The conditional part of this could be done with an enabled subsystem, where the output of the comparison (rotor angle >= particular value) enters the enable port of the enabled subsystem. Make it such that the enabled subsystem outputs 10% of the current load and subtract/add this signal to the corresponding area. Since the enabled subsystem is connected to the rotor condition will only output 10%*currentload if the rotor condition is true.
Above is a simplified version of what you could use. You take the difference in rotor angle and compare it to a value. Then you check your condition (change in rotor angle > value), if this is true then the enabled subsystem will run and take 10% of the current load. The outport1 would feed back to your model and be subtracted/added from/to the current load.
