use Data::Dumper;

my $VAR1 = { "baz" => [1,2,3,4] };
my $VAR2 = $VAR1;

print "BEFORE\n", Dumper($VAR1, $VAR2);

# Note $VAR1 is changed, but $VAR2 is still the hashref.
replace_ref($VAR1);

print "AFTER\n", Dumper($VAR1, $VAR2);

sub replace_ref {
	$_[0] = $_[0]{baz};
}