#!/usr/bin/perl
use strict;
use warnings;
use Data::Dumper;

my %base_data;
$base_data{test} = {
	k1 => {
		k1 => 1, 
		k2 => 2,
	},
};

my $add_data = {
	k2 => {
		k1 => 1, 
		k2 => 2,
	},	
};

# eleganter?
for my $key (keys %$add_data) {
	$base_data{test}{$key} = $add_data->{$key};
}

print Dumper $base_data{test};