code: public function getLayoutUpdatesFiles($storeId, $designArea)
      {
          $updatesRoot = $this->getConfig()->getNode($designArea . '/layout/updates');
  
          // Find files with layout updates
          $updateFiles = array();
  
          /** @var Mage_Core_Model_Config_Element $updateNode */
          foreach ($updatesRoot->children() as $updateNode) {
              if ($updateNode->file) {
                  $module = $updateNode->getAttribute('module');
                  if ($module && Mage::getStoreConfigFlag('advanced/modules_disable_output/' . $module, $storeId)) {
                      continue;
                  }
                  $updateFiles[] = (string)$updateNode->file;
              }
          }
          // custom local layout updates file
          $updateFiles[] = 'local.xml';
  
          return $updateFiles;
      }
docs: Returns all xml files that contains layout updates.
  
  @param int    $storeId store identifier
  @param string $designArea
  @return array