I suspect this is not possible without some programming effort (VB or C#).
You can customize the context menu, but this involves adding, moving and changing actions of options on the context menu. I am not aware of a way to replace the context menu completely with a single action of "reply to email".
I think this could open up the possibility of other problems/risks if you do this.
If you want a one click solution, if the email is opened simply click reply. If you are looking at the list of emails, select the one you want and click reply.
