Yeah the 30 minute extension is automatic and holds no caveats, longer than 30 minutes and they will contact the pic to see if they'll accept the extension. My experience with PSA is that they usually only check with the Captain then assume the rest of the crew falls in with his or her decision.

That being said the only way to not accept the extension without talking to a chief is to call fatigued which is a pretty simple and painless process in my experience.