Load CF7 CSS and JS only on a per need base

functions.php

add_filter( 'wpcf7_load_js', '__return_false' );
add_filter( 'wpcf7_load_css', '__return_false' );

function reregister_cf7_js() {
  if ( is_page (array(1,'kontakt'))) {
    if (function_exists( 'wpcf7_enqueue_scripts')) {
      wpcf7_enqueue_scripts();
      }
    if (function_exists( 'wpcf7_enqueue_styles')) {
      wpcf7_enqueue_styles();
      }
    }
  }
add_action('wp_enqueue_scripts','reregister_cf7_js');