Option to customize email designs

Button yes, button no, what link and text should the button have? These emails are sent to our customers from us, and I can't even modify the Subject of my templates without having to create a new one from zero.

Even if I create a new one from zero, there are no design customization options, only text to be added or changed. It would be a very useful feature to be able to modify the email designs, or at least let us use the button whatever way we need in each case...