Library /sys$common/syshlp/nclhelp.hlb set, session_control, application, user_name  *Conan The Librarian (sorry for the slow response - running on an old VAX)

    Default: None          Data type: Latin1String

    Identifies the default account under which the application is to
    run. For OpenVMS, if null then system defaults are used to select
    the user. The username must be specified in quotes on OpenVMS.

    Example:

    set session control application cml user name "cml$server"