I would like to have the registration emails, which are normally send to the emailaddress which is in the configuration.php file (like This e-mail address is being protected from spambots. You need JavaScript enabled to view it ), also been send to another emailaddress (like This e-mail address is being protected from spambots. You need JavaScript enabled to view it ). But ONLY registration emails should be send to this secundary emailaddress ( This e-mail address is being protected from spambots. You need JavaScript enabled to view it ) and not all other emails send to 'admin' ( This e-mail address is being protected from spambots. You need JavaScript enabled to view it ).
Is this possible and if yes, how?

No, it's not possible out of the box. You could use document subscriber incubator project CB Emails to customize an email to be sent to anyone you want with any information you want (fully supports substitutions) after registration.