Edit History

Puedes cambiar el orden en el que se muestran en el módulo por defecto a que sea aleatorio bastante fácil:

en /modules/ps_imageslider/ps_imageslider.php cambia:

$slides = Db::getInstance(_PS_USE_SQL_SLAVE_)->executeS('
    SELECT hs.`id_homeslider_slides` as id_slide, hss.`position`, hss.`active`, hssl.`title`,
    hssl.`url`, hssl.`legend`, hssl.`description`, hssl.`image`
    FROM '._DB_PREFIX_.'homeslider hs
    LEFT JOIN '._DB_PREFIX_.'homeslider_slides hss ON (hs.id_homeslider_slides = hss.id_homeslider_slides)
    LEFT JOIN '._DB_PREFIX_.'homeslider_slides_lang hssl ON (hss.id_homeslider_slides = hssl.id_homeslider_slides)
    WHERE id_shop = '.(int)$id_shop.'
    AND hssl.id_lang = '.(int)$id_lang.
    ($active ? ' AND hss.`active` = 1' : ' ').'
    ORDER BY hss.position'
);

por (sólo cambia la última línea):

$slides = Db::getInstance(_PS_USE_SQL_SLAVE_)->executeS('
    SELECT hs.`id_homeslider_slides` as id_slide, hss.`position`, hss.`active`, hssl.`title`,
    hssl.`url`, hssl.`legend`, hssl.`description`, hssl.`image`
    FROM '._DB_PREFIX_.'homeslider hs
    LEFT JOIN '._DB_PREFIX_.'homeslider_slides hss ON (hs.id_homeslider_slides = hss.id_homeslider_slides)
    LEFT JOIN '._DB_PREFIX_.'homeslider_slides_lang hssl ON (hss.id_homeslider_slides = hssl.id_homeslider_slides)
    WHERE id_shop = '.(int)$id_shop.'
    AND hssl.id_lang = '.(int)$id_lang.
    ($active ? ' AND hss.`active` = 1' : ' ').'
    ORDER BY rand()'
);

y luego cambia:

public function renderWidget($hookName = null, array $configuration = [])
{
  	if (!$this->isCached($this->templateFile, $this->getCacheId())) {
  		$this->smarty->assign($this->getWidgetVariables($hookName, $configuration));
	}

	return $this->fetch($this->templateFile, $this->getCacheId());
}

por:

public function renderWidget($hookName = null, array $configuration = [])
{
  	$this->smarty->assign($this->getWidgetVariables($hookName, $configuration));
	return $this->fetch($this->templateFile, $this->getCacheId());
}

et voilà!

P.S. Lo mejor es hacer esto con un override, para no perder los cambios cuando actualices el módulo.