Hi XU,
I understand that you are want to modify the resistance and capacitance of the three-phase parallel RLC Load.
As of now, there is no direct way to change these parameters but you can adjust all the parameters that are affected by resistance and capacitance which are Active power and Capacitive reactive power.
Also, I am providing a link to the documentation that will guide you through the process of configuring power parameters effectively: https://in.mathworks.com/help/sps/powersys/ref/threephaseparallelrlcload.html
