How to work with a hard drive directly?

Question

Hard disks

There is a PBDownforce program by

clicking on the "Start spoofing" button, it replaces the manufacturer of the hard drive and its serial number. After monitoring its actions, it opens and changes the contents of the file located along the path /device/Harddrive0/D and stops working with this file.
So the question is:
How and in what way can you work with a hard drive directly, as PB Downforce does?
i.e. go along the path / device / Harddrive0 / D and see at least what is there?