Filter to adjust the generated code for the Affiliates Add On.

custom_suffix_pmpro_affiliates_new_code.php

<?php
/**
 * Filter to adjust the generated code for the Affiliates Add On.
 *
 * You can add this recipe to your site by creating a custom plugin
 * or using the Code Snippets plugin available for free in the WordPress repository.
 * Read this companion article for step-by-step directions on either method.
 * https://www.paidmembershipspro.com/create-a-plugin-for-pmpro-customizations/
 *
 */
function custom_suffix_pmpro_affiliates_new_code( $code ) {
	return $code . '-AFF';
}
add_filter( 'pmpro_affiliates_new_code', 'custom_suffix_pmpro_affiliates_new_code' );