green light main site, private subsites

Hello, thank you for this. Is there a way to make the main site public, and at the same time, use the network setting override to make all the subsites visible to registered users only? I am trying to provide a private sandbox site for users, but at the same time, I want the main site to be accessible. I don’t want the individual subsites to be able to change the option, so I am stuck with enabling the network wide setting. Thanks!