Another option to customize import behavior is listening for events. The bundle fires following events during the import process:
Pimcore\Bundle\DataImporterBundle\Event\DataObject\PreSaveEvent: Fired just before an imported data object will be savedPimcore\Bundle\DataImporterBundle\Event\DataObject\PostSaveEvent: Fired just after an imported data object is savedPimcore\Bundle\DataImporterBundle\Event\DataObject\ProcessElementExceptionEvent: Fired when an exception is thrown when processing an element
More events to come when needed (just provide PRs ;-) .