Question: The private school I currently attend only allows for each student to take no more than two AP classes each year. However, I wish to take more AP courses while I am in high school. Would it be wise to participate in a postgraduate program at another school to increase my chances in getting into a selective college?
If your school has a good track record of getting its graduates into the kinds of colleges you're targeting, then it's probably not necessary for you to augment your school curriculum with outside APs. It is a bit unusual for a school to limit the number of APs, but the intent may be to keep the workload at manageable levels. I don't know what the rationale may be.