How filter the rate calculation

Note: Please copy and paste this code in functions.php of your current theme.

    function custom_wpcsr_shipment_cost_callback( $cost, $rate_id, $package_weight, $protection, $shipment_id ){
    $rateInfo = get_wpcsr_rate_by_id( $rate_id );
    $new_total_cost = 0;

    // Check if it is Cost per Weight
    if( $rateInfo->rate_type ){
      // Check if the Weight Cost is not 0
      if(  $rateInfo->weight_cost && (float)$rateInfo->weight_cost > 0 ){
            $new_total_cost += ( ( $package_weight - (float)$rateInfo->min_weight ) * (float)$rateInfo->weight_cost );
        }
    }
    // Else it is Flat Rate
    else{
      $new_total_cost = $rateInfo->price;
    }
    // Add the Protection/Insurance to the New Total Cost
    if( (int)$protection == 1 ){  
          $new_total_cost += (float)$rateInfo->rate_protection;
    }
    return $new_total_cost;
  }
  add_filter('wpcsr_shipment_cost', 'custom_wpcsr_shipment_cost_callback', 10, 5 );