update text within html
What you are thinking about, and moving toward (whether you know it or not) is called a content management system.
Most of them store content in a database and provide a user interface to allow editing it, just as you're designing.
Perhaps you could use off-the-shelf parts? I don't know exactly which ones are appengine-based, but this is a very common task and I'm sure you'll save time by using others' work.
So I have a python webapp on Google App Engine and am using the jinja2 template engine.  I have a lot of text on the site that I want to update regularly, such as news sections and updates about the site.
What is the most efficient way to go about doing this?  Clearly the simplest short-term solution and what I am currently doing is just to change the HTML but I would like to give others access to this without giving them access to the server side of things.
Should I just bite the bullet and write a interface on an admin page that allows users to edit it and then the server takes this and renders it in the News section? Any suggestions or tips would be great!