Looking to change the default “Your email address will not be published. Required fields are marked *” text that appears above the input fields in WordPress comment form?

Use the following code snippet:

add_filter( 'comment_form_defaults', 'my_comment_form_defaults' );
/**
 * Customize the text prior to the comment form fields.
 * @param  array $defaults
 * @return $defaults
 */
function my_comment_form_defaults( $defaults ) {

    $defaults['comment_notes_before'] = '<p class="comment-notes">'. __( 'Your email address will not be published. Required fields are marked *', 'my-text-domain' ).'</p>';

    return $defaults;

}

Change/set your desired text in the above.

One of the several ways in which this code can be added is as a new Snippet when using the Code Snippets plugin. Set the code to appear on frontend only.

Source: https://gist.github.com/ramseyp/8812696