Gnome-vfs API accessing system default MIME database ?

["725eb0c8ef771c09ee" <zjc99 mails tsinghua edu cn>]

Hi all,

As I know, GnomeVFS maintains system default MIME database, 
and user specific MIME database, which are located at /usr/share/mime-info, 
and .gnome/mime-info.

But seems that GnomeVFS only provides API to access/modifying the 
user-specific MIME database, but couldn't modify system default MIME data.

Is it possible to use GnomeVFS API to modifying the system default
MIME data ? Or, is there any other API to make it ?

Any help is appreciated.Thanks.
Daniel Z.