You bring up some excellent points MF , regardless of how tedious it may seem the best approach is a cautious one, make your changes one at a time and check to make sure your change had the desired effect and causes no errors, if you make a series of changes and get errors you will not be sure of which change is causing the error and you will be forced to start over, I have gotten in the habit of making a zip(as a back up of sorts) of my files after I complete all the changes I want to make and assure they are functioning properly, then when I make more changes for some reason if something does not work I have the original working file at my disposal.