/sys$common/syshlp/helplib.hlb REPLY, Qualifiers, /TO  *Conan The Librarian (sorry for the slow response - running on an old VAX)

       /TO=identification-number

    Requires OPER (operator) privilege.

    Sends a message to the user or file system specified by the
    identification number and completes the request. The current
    terminal must be enabled as an operator terminal.

    Note that you can also use a variation of the REPLY/TO command
    in response to a MOUNT/ASSIST command where you redirect the
    mount operation to another device. Whenever you must substitute
    a device, load the user's volume on the alternate device and
    prepare the device for connection before entering the REPLY
    command. Use the following syntax:

    REPLY/TO=identification-number "SUBSTITUTE  device-name"

    You can abbreviate the word SUBSTITUTE to S and can use uppercase
    or lowercase characters. After a space, use the remainder of the
    message-text space to name the substituted device.