My first instinct is to tell you to centralize these emails either in a text file or database and have your various programs go grab the values as needed. This would give you a central point where you can make updates.

Having said that you may have good reason not to take the above approach (although one escapes me right now). In that case I would write a script that takes 2 args (oldEmailAddress newEmailAddress) and loops through all of my source code files using a regex to update them. I'm not sure how an external program would know to do this unless you were able to modify it as well but good luck.