use strict;
use warnings;
use Data::Dumper;

my %HoH = (
    flintstones => {
                   lead => "fred",
                   pal => [ "george", "jane", "elroy" ],
    },
    jetsons => {
                  lead => "george",
                  wife => [ "george", "jane", "elroy" ],
                  boy => [ "george", "jane", "elroy" ],
    },
    simpsons => {
                  lead => "homer",
                  wife => [ "george", "jane", "elroy" ],
                  kid => [ "george", "jane", "elroy" ],
    },
);


my $key   = 'flintstones';
my $value = 'Wilma';

printf "Before:  %s\n", Dumper(\%HoH);

$HoH{$key}{"name"} = $value;

printf " After:  %s\n", Dumper(\%HoH);

__END__
Output (Note that 'Wilma' was successfully added):

Before:  $VAR1 = {
          'simpsons' => {
                          'kid' => [
                                     'george',
                                     'jane',
                                     'elroy'
                                   ],
                          'lead' => 'homer',
                          'wife' => [
                                      'george',
                                      'jane',
                                      'elroy'
                                    ]
                        },
          'jetsons' => {
                         'lead' => 'george',
                         'wife' => [
                                     'george',
                                     'jane',
                                     'elroy'
                                   ],
                         'boy' => [
                                    'george',
                                    'jane',
                                    'elroy'
                                  ]
                       },
          'flintstones' => {
                             'lead' => 'fred',
                             'pal' => [
                                        'george',
                                        'jane',
                                        'elroy'
                                      ]
                           }
        };

 After:  $VAR1 = {
          'simpsons' => {
                          'kid' => [
                                     'george',
                                     'jane',
                                     'elroy'
                                   ],
                          'lead' => 'homer',
                          'wife' => [
                                      'george',
                                      'jane',
                                      'elroy'
                                    ]
                        },
          'jetsons' => {
                         'lead' => 'george',
                         'wife' => [
                                     'george',
                                     'jane',
                                     'elroy'
                                   ],
                         'boy' => [
                                    'george',
                                    'jane',
                                    'elroy'
                                  ]
                       },
          'flintstones' => {
                             'lead' => 'fred',
                             'name' => 'Wilma',
                             'pal' => [
                                        'george',
                                        'jane',
                                        'elroy'
                                      ]
                           }
        };