This assumes your app already has some views for live output, and now you want to work on a copy of this in the background without normal users seeing errors. 

This checklist assumes that your initial templates in the root folder. 

Setup

1. Create a new folder called live and move your templates to that folder. You will also need to re-adjust the view configuration to point to these files. 
2. Copy the live folder and call the copy staging. These will be your dev files. Make som minor changes in the text so you can tell when you see them. 
3. Activate Super-User Polymorphism
4. Test to verify switching works

You can now make your changes to the copied templates as needed. 

Deploy Changes

Once you are happy with your changes, you can copy the files from staging to live so your users see what you did.