I'm not sure how you pick the 'rg' for a given two digit prefix. (e.g. Why is it 22 => rg1003 and not 22 => rg1000.) Do you pick the most popular 'rg' for the given prefix? If so, the following will do the trick:

my %pop;

++$pop{substr($_, 0, 2)}{$numbers{$_}}
   foreach keys %numbers;


my %most_pop;

foreach my $short (keys %pop) {
   my $short_pop = $pop{$short};
   my ($most_pop) = sort { $short_pop->{$b} <=> $short_pop->{$a} }
                    keys %$short_pop;
   $most_pop{$short} = $most_pop;
}


my %filtered;

foreach (keys %numbers) {
   my $key      = $_;
   my $rg       = $numbers{$_};
   my $short    = substr($_, 0, 2);
   my $most_pop = $most_pop{$short};

   if ($rg eq $most_pop) {
      $filtered{$short} = $most_pop;
   } else {
      $filtered{$key} = $rg;
   }
}

print("$_ => $filtered{$_}\n")
   foreach sort keys %filtered;
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