How to programmatically copy Webform handler config?
Ended up using the ConfigFactory service, which I believe is fine to do:
$config = \Drupal::configFactory()-&gt;getEditable('webform.webform.' . $webform-&gt;id());
$config_key = 'handlers.' . $webform_handler_id;
$config-&gt;set($config_key, $new_handler_config)-&gt;save();