You could do something like the following:

my %users;

my %rank_order = (
   Leader     => 1,
   Chairman   => 2,
   Lieutenant => 3,
   Veteran    => 4,
   Rookie     => 5,
);

sub by_hi_rank {
      $rank_order{$users{$a}{title}} <=> $rank_order{$users{$b}{title}
+}
   || $a                             cmp $b
}

sub by_lo_rank {
      $rank_order{$users{$b}{title}} <=> $rank_order{$users{$a}{title}
+}
   || $a                             cmp $b
}

my %sorters = (
   by_rank => {
      ascending  => \&by_hi_rank,
      descending => \&by_lo_rank,
   },
   by_user => {
      ascending  => sub { $a cmp $b },
      descending => sub { $b cmp $a },
   },
);

my $sorter = $sorters{$criteria}{$order}
   or die;

my @sorted_users = sort { $sorter->() } keys %users;
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