How do I opt out - exit from the pilot program after I join in (both before and after prosecution begins)?

Once the Application has been published as part of this program on the Peer-to-Patent web site it continues to be open/available for comments for peer reviewers.

Applicants may expressly abandon their application; however, the application may continue to received comments from the public due to its publication on the Peer-to-Patent website as the website is not managed by USPTO.

USPTO FAQ - Questions and Answers (25JUN2007)