Would be helpful to have this same choice to change the send from (Send as) option in the Send email with options action.
This would not be the helpful thing to send the email as "Send as" because this will allow the user to mask their identity or username. This can be a threat to email security. There will be no use of a unique username. If you still have some doubts I recommend you to go to Optimum Customer Support, you will know why it can not be done so.