[WordPress] Add capability for single user or role

add-capabilities.php

add_action( 'admin_init', 'add_theme_caps');
function add_theme_caps() {
  // add single role capability
  $role = get_role( 'administrator' );
  $role->add_cap( 'manage_phrases' );
  // add single user capability
  $user = new WP_User( 4766 );
  $user->add_cap( 'manage_phrases' );
}