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add_filter( 'tribe_the_notices', 'customize_notice', 10, 2 );
function customize_notice( $html, $notices ) {
	// If text is found in notice, then replace it
	if( stristr( $html, 'This event has passed.' ) ) {
		// Customize the message as needed
		$html = str_replace( 'This event has passed.', 'This event is gone but will not be forgotten.', $html );
	}

	return $html;
}