If you have a static text and it is the same for all vendors, you can overwrite the template and add it to any suitable position, please check this doc: How to customize templates - HivePress Help Center.
Is there a way to edit the current orders template without having to build it from scratch again like in the video?
For instance, I want my starting point on my New Template → Orders to be what it already is right now, so the only thing I have to do is add the text/instructions somewhere on the order receipt?