automatically add custom fields to post title

You could write a function to hook into the display of the title, and then when the title is displayed, it will get the value of the custom field and append it to the title. That way you aren’t editing/changing the title every time you save the post.

You could do something like:

function append_year( $title ) {
    global $post;
    $terms = wp_get_post_terms( $post->ID, 'release-year', array("fields" => "names") );

    if ( count( $terms ) ) {
        return $title . '(' . $terms[0] . ')';
    } else {
        return $title;
    }
}

add_filter( 'the_title', array($this, 'append_title' ) );

wp_get_post_terms returns an array, and you can pass it an array of args to configure what you want see the wp_get_post_terms documentation.

The code above was adapted from this other SO post about appending title text