An example of how to adjust the commission for one specific item in a referral's order.

abcstore_module.php

<?php
 
class AbcStore_Module extends Core_ModuleBase
{
  public function subscribeEvents()
  {
    Backend::$events->addEvent('threetwentynyaffiliate:onGetReferralCommission', $this, 'on_get_referral_commission');
  }
  
  public function on_get_referral_commission($referral, $original_commission)
  {
      $order = $referral->order;
      $commission = $original_commission;
      foreach($order->items as $item) {
          if ($item->product->sku == 'your-product-sku') {
              $old = $item->single_price * $referral->commission_percentage * .01; //Figure out old commission
              $new = $item->single_price * .02; // Low 2% commission for this product
              $commission -= ($old - $new); // Subtract the difference
          }
      }
      return $commission;
  }
  
}