The macro is a function intended to be used as a custom process with the linked add-in, which handles the folders. You select the folder(s) from the add-in.
As for the code listing. This is installed in the normal template - see
http://www.gmayor.com/installing_macro.htm
You can then enter its name 'NewFooter' in the Custom Process dialog of the add-in. See my web page linked in the previous post for more details.
You can use it with the current document; a folder full of documents; or a folder full of documents and all its sub folders.
It works by examining all the footer ranges in the document(s) to check for the replacement text, and the original text. If the original text is present and the replacement text is not, then the replacement is added to the original as you requested.