This terse approach may hint at future possibilities for text file hackery:

perl -M5.010 -Mstrict -F, -wanle '
    BEGIN{ $" = "," }
    our ($rpt, $non_key);
    if ( ($non_key // "") eq "@F[1..5]"){
        print; # this line not right - exercise left to reader
    }
    else {
        $rpt = $F[4] -1;
        $non_key = "@F[1..5]";
        print
    }
'
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