With regards to closing out your original foreach loop and starting a new one, that's exactly what I don't think you should do. It's possible, but it makes your code more complicated than it needs to be.

In the code you've given, you've got two separate foreach loops, each one having internal if-structures. Simply move all of the if-structures into a single large foreach loop, i.e.:

foreach my $row ($sheet->{MinRow}+18..$sheet->{MaxRow}){

    if ($sheet->{Cells}[$row][2]->{Val} eq "SYSTEM") {$comment = $shee
+t->{Cells}[$row-2][2]->{Val};}
    if ($sheet->{Cells}[$row][3]->{Val} eq "UPGRADE SOLUTION") {$upgra
+de=1} else {$upgrade=0};
    if ( $sheet->{Cells}[$rw][0]->{Val} =~ /(^\d+)/ ) {
    
     $line = $sheet->{Cells}[$rw][0]->{Val};
     $qty = $sheet->{Cells}[$rw][1]->{Val};
     ...
[download]

Doing that should make sure that $comment is set appropriately each time you get to a detail line, without the need for any more than the single, large foreach loop.