Change FROM and REPLY TO address

Hello, I am trying to change FROM and REPLY TO addresses when user sends example email (“Send Example” button in email view).
I have created Bundle/EventListener/BuilderSubscriber.php which contains onEmailGenerate() method and it is being called when user sends example email. This method changes FROM and REPLY TO addresses, so it seems OK (by looking at debug logs). But I received example email which FROM and REPLY TO addresses has not been changed. So it is being defaulted back. What I am missing? What changes it back? What would be correct way to do so?

BuilderSubscriber.php code: