$dword  = pack <somehow> ( $value );   # eg $value = 5242880 dec

    $mask   = pack <somehow> ( 4194304 );  # 0x00400000
    $flags  = pack <somehow> ( 1048576 );  # 0x00100000

    $testdw = $dword & $mask;
    $newdw  = $dword | $flags;
    $newval = hex ( $newdw );   # gets written to file