Feature summary (what you would like to be able to do and where):
I propose the addition of the following parameters:

• preloadcategories[]=: List of categories to append to the page
• prependtext=/appendtext=: Text that would be prepended resp. appended to the page

Technical considerations
Instead of adding the content to the page while saving, this could also just be added when preloading the edit form, but in this case, we would risk that the user deletes that (I'm sure there are both cases where this would be considered a benefit and some in which it would be considered a deficit)

Use case(s) (list the steps that you performed to discover that problem, and describe the actual underlying problem which you want to solve. Do not describe only a solution):
Sometimes, we want to add content no matter what the user provides in the edit form (or if we use T382667 and said content cannot be added via the template automatically)

Benefits (why should this be implemented?):