VMS Help Sys Parameters, ACP_BASEPRIO  *Conan The Librarian (sorry for the slow response - running on an old VAX)

    ACP_BASEPRIO sets the base priority for all ACPs. The DCL command
    SET PROCESS/PRIORITY can be used to reset the base priorities of
    individual ACPs. ACP_BASEPRIO is not applicable for XQPs.

    ACP_BASEPRIO is a DYNAMIC parameter.