#!/usr/bin/perl --

use strict;
use warnings;

my $hash = {
   one => [ 1],
   two => [ 2],
};

$hash->{one}[2] = "three";

use Data::Dumper;
print Dumper($hash);
__END__
$VAR1 = {
          'one' => [
                     1,
                     undef,
                     'three'
                   ],
          'two' => [
                     2
                   ]
        };