It's likely that the text file is intended to be altered only by changing settings in the IDE GUI.
This is incorrect. There is only one rather brief preferences 'page' in the IDE, and at the bottom it states "More preferences can be edited directly in the file <path>".
I could be wrong, but isn't the IDE open source?
The Arduino is intended to be very easy for programming novices to use. I don't think it's reasonable to expect them to wade through large amounts of intricate java code to try and work out from it, perhaps partly by 'reverse engineering', what preference options are available and what they do.
If the options are clearly documented in one or more places in this code then I suggest that the content of this documentation should be made available directly from the Arduino IDE and/or the Arduino website.