Library /sys$common/syshlp/sysmanhelp.hlb IO, REBUILD, Qualifiers, /VERIFY  *Conan The Librarian (sorry for the slow response - running on an old VAX)

    Causes SYSMAN to read and process the files SYS$SYSTEM:SYS$USER_
    CONFIG.DAT and SYS$SYSTEM:CONFIG.DAT, but not to apply the files
    to the I/O database. Messages will be displayed for any errors
    that are encountered. This command can be used by developers
    to test new changes to SYS$SYSTEM:SYS$USER_CONFIG.DAT without
    modifying the current system.