Do you see yourself creating and modifying data layers every time you implement a new tracking via Google Tag Manager?
If yes then this article is for you. I will show you how to create universal data layers that will save you from adding/editing data layers over and over again for different tracking requirements.
Consequently you have to make changes to your data layers. The volume and type of changes that you actually need to make depend upon the CMS and shopping cart you are using as well as your tracking objectives. But you have to make changes.