Kinda sorta not really. It all depends on whether what you're modifying is the stuff in the hash you copied or in child hashes. Let's say you have:

my %hash = (
    key1 => {
        a => 1,
        b => 2,
    },
    key2 => 'blah'
);

my %hash1 = %{ $hash{key1} };

$hash1{a} = 3;    # This change persists
$hash1{c} = 5;    # This change does NOT persist
[download]

It all depends, doesn't it? :-) (And also why objects should encapsulate this crap.)

------
We are the carpenters and bricklayers of the Information Age.

Don't go borrowing trouble. For programmers, this means Worry only about what you need to implement.