woo_bugger.php

<?php

add_action( 'woocommerce_before_calculate_totals', 'add_custom_price', 0 );

function add_custom_price( $cart_object ) {
    $custom_price = 100; // This will be your custome price



    $cart_object->recurring_cart_key = '2016_10_11_every_3rd_month';
    foreach ( $cart_object->cart_contents as $key => $value ) {

        $value['recurring_cart_key'] = '2016_10_11_every_3rd_month';
        $value['next_payment_date'] = '2016-07-11 15:23:20';
        $value['data']->parent->subscription_period_interval = '3';
        $value['data']->parent->product_custom_fields['_max_variation_period'] = '3';
        $value['data']->parent->product_custom_fields['_max_variation_period_interval'] = '3';
        $value['data']->parent->product_custom_fields['_subscription_period_interval'] = '3';
        $value['data']->price = $custom_price;
    }
    echo "<pre>";
      var_dump($cart_object->cart_contents['6256c1088a58b28901d15330d8d4fb8e']['data']->parent->subscription_period_interval);
    echo "</pre>";
}