my %bighash = (
     'A' => 1,
     'B' => 2,
     'C' => 3
);

##</code><code>##

$bighash{'C'} = 'some new value';
$bighash{'D'} = 4;

##</code><code>##

%bighash = ( %bighash,
     'C' => 'some new value',
     'D' => 4
);