Skip OSX Beta Update
Yes. You get prompted to install each build, so don't click for beta 3. Once 4 arrives, you'll likely have to first jump to 3 and then jump to 4. 

This is documented at http://openradar.appspot.com/22307567

Your comment about not opting out is also confusing - I'm not sure how that relates to your ability to choose whether to install a specific update.