How can I abort Software Update safely?

I made the mistake of clicking on Software Update when millions of people around the world are trying to update their iPhones and iPads at the same time. I thought I was just updating iTunes, but it turned out to be iTunes plus OS 10.8.5 plus a bunch of content for Motion totaling 1.55 GB. Progress bar says more than seven days to go and won't let me quit AppStore. What happens if I try to Shut Down or Force Power Down during this OS related download?