Thanks for the question and I'm excited about your son's progress. Certainly bump up to the college schedule. The HS schedule assumes your son may play a fall sport, but that's not always the case with every pitcher who's following the program and continuing to train as outlined in the College plan is what I recommend.
Still try to find 2-3 months off from throwing in your son's schedule. The fall and early winter is generally the best time for this break as he continues to condition, strength train and build flexibility.
If you have any additional questions, please feel free to email me directly.