@PradeepPydi - You have to disable the agent from the agent schedule instances. For each of the agent/node combination present in the cluster Pega will create an agent schedule instance. You have to manually go and disable it from there. Once you do it post restart it will not turn on automatically.
If your node id changes anytime due to movement of temp directory or system name change then new agent schedule rules will be created and you will have to repeat the exercise.