Hi there,
Thanks for writing in! Unfortunately, this isn’t a feature of the Templates option. Also saving templates as pages will replace what’s on the current page when loaded. Using Template pages is good for when you are just starting out. Now if you want to append content use template blocks instead. However, there is no option to dynamically link multiple instances of these page templates or blocks so that they can all be updated at once.
Hope this helps clarify – thanks!