If I open Window Explorer and right-click Libraries\Documents or Music or Pictures or Videos, select properties I can remove the links directing to the C drive and enter the drive, directory and sub-directory I want. Then all Microsoft Office software use by default the directories I have written. Clicking any component of Libraries (Documents, Music, Pictures, Videos) point to the directories I want.
But desktop is something different. It’s always in your eyesight. When downloading, selecting Desktop icon may produce similar results. But it doesn’t prevent anybody to copy a file and right-click on actual desktop and select paste. It must be something about the rights of users.
BTW I use Win7 Ultimate 64 bits.
Thank you to everybody who have answered