Changing the page title in WordPress

//CHANGE POST TITLE
function custom_modify_title( $title, $id = null ) {
        return 'CUSTOM '.$title;
    }
add_filter( 'wp_title', 'custom_modify_title', 10, 2 );
add_filter( 'the_title', 'custom_modify_title', 10, 2 );

Change depending on post type

//CHANGE POST TITLE
add_filter('the_title','custom_modify_title2');
function custom_modify_title2($data){
    global $post;

    if (get_post_type( $post->ID ) == "expertenprofil") {
      return get_post_meta($post->ID, 'wpcf-anonymer-titel', true);
    } else {
      return;
    }
}

Changing document title

//CHANGE POST TITLE
add_filter( 'pre_get_document_title', 'change_profile_title' );
function change_profile_title () {
	global $post;

	if (get_post_type( $post->ID ) == "expertenprofil") {
		return get_post_meta($post->ID, 'wpcf-anonymer-titel', true);

	} else if (get_post_type( $post->ID ) == "bewertung") {

		//bewertung nutzt sowieso anonymen titel daher brauche ich das nicht
		// get the id of the post
		/*
		$the_id = $post->ID;
		// get the custom taxonomy term name
		$source_archive_name = wp_strip_all_tags( get_the_term_list( $the_id, 'bundesland', '', ' / ' ) );
		// read all the data for the term into an array
		$term_data = get_term_by( 'name', $source_archive_name, 'bundesland', ARRAY_A );
		// pull the term id out of the array
		$term = get_term( $term_data["term_id"], 'bundesland' );
		$bundesland = $term->name;
		return "Einigungsstelle in ". $bundesland;	
		*/
		//return $post->post_title;
		return;

	} else {
		return;
	}
}