permanently modify a hash key?

[Mark Hanson]

Hi!

Yet another hash question:

How can I permanently modify a hash key? I have the following hash:

my %hash = (                         
        hygiene_products_total_amount => {    
                'conditioner' => "5", 
                'shampoo'       => "57",
                'soap'  => "1", 
        },                              
        cleaning_products_total_amount => {   
                'mops' => "20",            
        },                              
);    

I tried the following which prints out the correct value, but doesn't permanently 
modify the key.

#removing all but two underscores
foreach (keys %hash) {                         
        $count = $_ =~ s/(_)/$1/gi;               
        while (($count = $_ =~ s/(_)/$1/gi) > 2) {
                $_ =~ s/_//;                      
        }                                         
print "\n$_\n";                                   
}           

Any help is appreciated. Thanks!

/Mark