How do you discipline a 3 yo with sensory processing disorder?

My 3 yo has SPD, and I don't want to punish him too harshly. We do not in our house. I have a hard time deciphering between him not being able/aware of what he is doing, and the times he is doing it just to do it. How do you deal with this. This is very new to us, as he was just diagnosed 2 months ago. What are the boundaries as a parent I can set for him that he will understand, and i can expect him to be able to follow.