Adam, thanks for your reply - however that's not what I need. I think you misunderstood my question.

 

I handle the replacing before emails are sent, which is done maybe months after the email has been constructed...

 

What I need is something to assist the user while constructing the email.

 

The user might want to change the field {start_date_Long} to {start_date_short}. 

What needs to happen when the user clicks within the {start_date_Long} field is the entire field must be selected, thus preventing the user from manually editing the field text, which could lead to errors.

 

Consider the following:

{start_date_short} manually edited could end up being {start_date_shhort} because of human error.