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$center = field_get_items('node', $node, 'field_center');
$newnid = $center[0]['target_id'];

$cntr = node_load($newnid);
$address = field_get_items('node', $cntr, 'field_address');

$node->field_address[LANGUAGE_NONE][0]['country'] = $address[0]['country'];

field_attach_update('node', $node);