Command line / headless is a powerful tool, but it can and should be enhanced.
Here is a feature request that would be helpful to users and QA of LO.
Add option to update fields from command line - in GUI Writer, that's Tools-Update-Update All.
I disagree. Command line interface does not provide options to *control document contents* in any way. It allows to open, print, convert - i.e., tasks that intend to not change the content (conversion opens and saves, ideally keeping the content intact).
The suggested extension would be partial, and then you would need to add another command, and two more, and then all gazillions of UNO commands. But:
1. You may create a macro, and run it from command line;
2. You may create a script, and fully control LO from it.