Jason S. answered 07/18/19
Microsoft Word - Document Formatting & Professional Layout
You're correct in the method you're using to try to edit the Template and you will have to name it something different in order to save the edited Template. The documents that were created based on the Template won't be affected because the Template only affects how the documents look when they are first opened. Once the documents are saved as a Word document, they are completely separate files from the Template and have no connection of any kind to the Template.