I'm pretty sure the only option I had was a statement that basically said, "Click to restart your Nexus 7.2 and install Android 4.4." One option equals no option to opt out in this case. It was more like a statement that like it or not you are getting 4.4. I didn't try hitting the back button. Perhaps that would have worked for a short time, but I suspect that reminders would have been often an annoying until it finally updated.