Official comment
No, you don't have to edit all your web pages!
All of the settings on the "back end" of an order form, such as Rules, Sequences, and the payment Gateway will automatically be updated as soon as you make the change!
This is true regardless of what type of embed code you used (JavaScript, iFrame, HTML, etc.).
If you add additional fields or design changes to the "front end" of the form that you clients actually see you may have to re-install the form code. To see if you do, simply visit one of the Order Forms ... what you see is what you get in this case, and you'll be able to tell if you must re-embed the form code.