I disagree strongly. Config files being modified by anyone should be going through code review. The risk of not understanding while at the same time modifying things is extremely low.

Plus, the documentation in the application code that loads the config and manipulates would function as the exact same reference documentation for any developer trying to understand how the config is used or why a choice is made.

This prevents the documentation about what the config is supposed to be used for from being coupled with the implementation detail of what particular config file looks like, what language it’s written in, etc.

Just as you say, a config file is a stack of magic constants. They have no meaning at all sitting in that file. The place to look for their meaning is the documentation of the code that loads the file, which should tell the user everything they need to know about modifying or providing their own file.