Hi there - sorry for the latency in your post, our spam filters thought you’re an evil bot.
Unfortunately, there is not. Private posts and public posts are very different on the inside, and toggling the visibility would require your pod to send all of your posts to all of your contacts again. For older accounts with lots of posts and contacts, this could easily dispatch a million updates.
Yes! In your account settings (top right corner where your profile name is → settings), there’s a “Default aspects selected for posting” setting. You can set that to “public” and stop worrying about it.