$user_id = 5; $new_role = 'editor'; $user = new WP_User($user_id); $user->add_role($new_role);
$user_id = 17; $new_roles = array('editor', 'author'); $user = new WP_User($user_id); foreach ($new_roles as $role) { $user->add_role($role); }This code assigns the roles 'editor' and 'author' to the user with ID 17. Package library: WordPress core.