Are you referring to content templates in tinymce https://youtu.be/OyZQ63Ahnt4

If so then I cannot replicate that at all. As you state its just a simple cut/paste so what you describe is impossible.

its far from impossible. It's a feature REQUEST! if the article template was "hotlinked" where on article save it was automatically updated in some fashion.. plugin maybe?.. then anytime they edit the article template it would update the article.
or, articled template inserts ( for example ) {my article template] then its rendered at runtime just like [fields xx} are.
or lastly a method where {field xx} is processed if its inside a text area field.
so for example
field 3 = article template text area - Paste article template in "default value"
fiield 1 = name
field 2 = age

Article template

Hi {field 1} I see you are {field 2} years old

Article

{field 3}

Now the article template is completely dynamic!

Ah - it read that you were saying a change to the template changed the existing articles.

What you are asking for can be done. https://www.tiny.cloud/docs/plugins/opensource/template/

It's just a copy/paste with some xtras so your render at runtime would not be possible. It would also mean that the content is not searchable as it would not exist in th database.

Could someone add a new feature label please