Thx haukex for the precise explanation. I like to finish my threads with working code, for myself and presumably others who will search the net for why Data::Dumper doesn't work unless you 'use' it. They give a pretty good example here, and I wish that all modules would give example code snippets:

$ ./1.dd.pl
$VAR1 = [
          {
            '81' => 'QQQ',
            '80' => 'PPP',
            '79' => 'OOO',
            '78' => 'NNN',
            '77' => 'MMM',
            '76' => 'LLL',
            '75' => 'KKK',
            '74' => 'JJJ',
            '73' => 'III'
          },
          {
            '75' => 'KKK',
            '79' => 'OOO',
            '77' => 'MMM',
            '81' => 'QQQ',
            '73' => 'III'
          },
          {
            'III' => '73',
            'JJJ' => '74',
            'KKK' => '75',
            'LLL' => '76',
            'MMM' => '77',
            'NNN' => '78',
            'OOO' => '79',
            'PPP' => '80',
            'QQQ' => '81'
          }
        ];
$ cat 1.dd.pl 
#!/usr/bin/perl -w
use 5.011;
use Data::Dumper;

$Data::Dumper::Sortkeys = \&my_filter;
my $foo = { map { (ord, "$_$_$_") } 'I'..'Q' };
my $bar = { %$foo };
my $baz = { reverse %$foo };
print Dumper [ $foo, $bar, $baz ];
 
sub my_filter {
    my ($hash) = @_;
    # return an array ref containing the hash keys to dump
    # in the order that you want them to be dumped
    return [
      # Sort the keys of %$foo in reverse numeric order
        $hash eq $foo ? (sort {$b <=> $a} keys %$hash) :
      # Only dump the odd number keys of %$bar
        $hash eq $bar ? (grep {$_ % 2} keys %$hash) :
      # Sort keys in default order for all other hashes
        (sort keys %$hash)
    ];
}

$
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