Так ну тут уже понятно куда копать)
public function onContentPrepareForm(&$form, $data)
{
$app = JFactory::getApplication();
$name = $form->getName();
$layout = $app->input->get('layout');
if (!$app->isSite() || $name !== 'com_content.article')
{
return;
}
if ($data->attribs)
{
$data->attribs = json_decode($data->attribs, true);
}
$form->loadFile(__DIR__ . '/fields.xml');
$form->setFieldAttribute('title', 'size', '100');
$contentnoprogram = explode(',', $this->params->get('contentnoprogram', ''));
$data = (array)$data;
if(isset($data['catid']) && in_array($data['catid'], $contentnoprogram))
{
$form->setFieldAttribute('image_intro', 'directory', 'images/pages/intro', 'images');
$form->setFieldAttribute('image_fulltext', 'directory', 'images/pages/full', 'images');
}
else
{
$form->setFieldAttribute('image_intro', 'directory', 'images/icons', 'images');
}
}