Override EmailRepository

[sonjadeissenboeck]

I'd like to override the Email Repository to customize one function for my needs. Has anyone ever done this? I couldn't find any documentation on overriding an entity repository. Why I need to do: the DatabaseSpool Service calls the markCompleteSending() function from the repository. But I'd like to change one part of it.
What I tried: create an own Entity repository class:

namespace NotificationBundle\Entity;  
use Doctrine\ORM\EntityRepository; 
use Citrax\Bundle\DatabaseSwiftMailerBundle\Entity\Email; 
use Citrax\Bundle\DatabaseSwiftMailerBundle\Entity\EmailRepository as BaseRepository;  class EmailRepository extends BaseRepository {      
public function markCompleteSending(Email $email)     {         
$email->setStatus(Email::STATUS_COMPLETE);        
$email->setSentAt(new \DateTime());         
$email->setErrorMessage('');         
$em = $this->getEntityManager();         
$em->remove($email);         
$em->flush();     
} }

it extends the parent repository and overrides only this function, the rest I didn't touch. I then registered that repository as a service. Anyway it's not working!
Anything else needed? Please let me know! I'd be glad about some help.