VMS Help SET, PROCESS, Qualifiers, /PRIORITY  *Conan The Librarian (sorry for the slow response - running on an old VAX)

       /PRIORITY=n

    Requires ALTPRI (alter priority) privilege to set the priority
    higher than the base priority of the specified process.

    Changes the priority for the specified kernel thread. If you do
    not have the ALTPRI privilege, the value you specify is compared
    to your current base priority, and the lower value is always
    used.