WooCommerce 2.5+: add new variations settings

wc25.php

<?php

// Add New Variation Settings
add_filter( 'woocommerce_available_variation', 'load_variation_settings_fields' );

/**
 * Add custom fields for variations
 *
*/
function load_variation_settings_fields( $variations ) {
	
	// duplicate the line for each field
	$variations['text_field'] = get_post_meta( $variations[ 'variation_id' ], '_text_field', true );
	
	return $variations;

}