Inside your subroutine, you are making copies of the referenced arrays (@arr1 and @arr2 are the copies), and then you are modifying the copies. If you want to change the original arrays, you should modify the references directly, something like this:

sub changem {
    my ($r1,$r2) = @_;
    print "BEFORE: $r2->[1]\n";
    $r2->[1] = 'q';
    print "AFTER:  $r2->[1]\n";
}
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-- Mike

--
just,my${.02}