How to remove manually granted permissions on all archives

Hi,

We've granted permissions on all archives to a user (in our records management area) using the following script;

[Directory]
DirectoryComputerName = Vaultserver_that_hosts_directoryservice
SiteName = Sitename_from_admin_console

[ArchivePermissions]
ArchiveName = ALL_MAILBOX
GrantAccess = read write, Domain Name\User Name

How do we reverse it (i.e. remove this particular user's permission from all archives)?

Also can somsone advise whether or not its possible to grant an AD group read permission on all or selected archives and how?

Thanks, Saf