You can update your mailer return address from your Account page under the profile tab.
We don't currently have the functionality to use more than one return address. However, you can change your address in your account profile whenever you'd like. Be sure to update your return address before clicking on an address to start the process of sending mail. Note: if you are changing your address in another tab, make sure to refresh the tab that you are sending mail from in order for your browser to recognize the change.