Change the text that's posted to Facebook

When people RSVP for an event with Facebook, it automatically posts to their wall. I'd like to:
1. Edit the text that's posted. As you can see in the screenshot, it doesn't say "I just RSVP'd for..." or include any details that would make this post interesting or shareable. It also includes info from past events in the description, which should not be there.
2. Give the user the choice of whether or not the post is created
3. Turn off the auto-post altogether, if I can't do #1 and #2