Library /sys$common/syshlp/uafhelp.hlb MODIFY, Qualifiers, /UIC  *Conan The Librarian (sorry for the slow response - running on an old VAX)

       /UIC=value

    Specifies the user identification code (UIC). The UIC value is
    a group number in the range from 1 to 37776 (octal) and a member
    number in the range from 0 to 177776 (octal), which are separated
    by a comma and enclosed in brackets. Digital reserves group 1 and
    groups 300-377 for its own use.

    Each user must have a unique UIC. By default, the UIC value is
    [200,200].