functions.php

<?php

add_action( 'woocommerce_applied_coupon', 'change_subscription_next_payment_due_date' );
add_action( 'woocommerce_removed_coupon', 'change_subscription_next_payment_due_date_on_remove_coupon' );

function change_subscription_next_payment_due_date( $coupon_code ) {
	if ( 'bundle' === strtolower( $coupon_code ) ) {
		change_next_billing_date( 90 );
	}
}

function change_subscription_next_payment_due_date_on_remove_coupon( $coupon_code ){
	if ( 'bundle' === strtolower( $coupon_code ) ) {
		change_next_billing_date( 30 );
	}
}

function change_next_billing_date( $days ){
	if ( did_action( 'wp_loaded' ) && isset( WC()->cart ) ) {
		$contents = WC()->cart->get_cart();
		if ( ! empty( $contents ) ) {
			foreach ( $contents as $item_key => $item ) {
				$product = $item['data'];
				if ( ywsbs_is_subscription_product( $product ) && $product->get_id() === 12451 ) {
					$subscription_info = $item['ywsbs-subscription-info'];
					if ( $subscription_info ) {
						$subscription_info['next_payment_due_date']                       = time() + $days * DAY_IN_SECONDS;
						WC()->cart->cart_contents[ $item_key ]['ywsbs-subscription-info'] = $subscription_info;
					}
				}
			}
		}
	}
}