Theresa - I think this is really going to depend on your site and corresponding CMS if you are leveraging one. If you can share some of the specifics on your deployment we might have some users that give you some insight.
While you will eventually want to remove unnecessary code - your first action may not have to be a replace if it is more complicated then an insert/apply.
For instance if you are leveraging Drupal, you could insert at the theme level and have it apply across your property with that theme. Other CMS systems have similar functions.