Thank you for your inquiry.
Yes this is possible - In order to do this, you will have to create a new email template.
You will have to navigate to Document Templates / Dokumentvorlagen, in the navigation to your right.
After clicking on creating a new template, you will have to choose the template you would like to modify - a new window should open itself where you can modify several options regarding the template.
There should be an option called name where you can change the subject.
Let me know if you need anything else!