Changing the product price in the renewal order.

functions.php

<?php

add_filter( 'wcs_renewal_order_created', 'test_change_renewal_order_price', 10, 2 );

function test_change_renewal_order_price( $renewal_order, $subscription ) {

	// Get the line item for the subscription product
    $line_items = $renewal_order->get_items();

	foreach( $line_items as $line_item ) {
		// Set the new price
		$new_price = 19.99;
			
		// Update the line item price and total
		$line_item->set_subtotal( $new_price );
		$line_item->set_total( $new_price );
	}
    
    // Recalculate the order totals
    $renewal_order->calculate_totals();

	return $renewal_order;
}