Personalized message for each unique password-protected page

You should probably add in more checks, but this should get you started.

function change_pw_text($content) {

    // Just to save processing other pages.
    if ( !is_page('page-slug-one') && !is_page('page-slug-two') )
        return $content;

    $find = 'This post is password protected. To view it please enter your password below:';

    if ( is_page('page-slug-one') )
        $replace="Hint: Tell our system to show you, and it will.";

    if ( is_page('page-slug-two') )
        $replace="Sorry: This page requires you to be logged in.";

    $content = str_replace( $find, $replace, $content );

    return $content;
}

add_filter('the_content','change_pw_text');

For a nice resource on the possible Conditional Tags in WordPress see… http://codex.wordpress.org/Conditional_Tags