gistfile1.php

<?php
/**
 * Change the referral email
 */
function affwp_emails_referral_email( $message, $args ) {
	
	$email    = affwp_get_affiliate_email( $args['affiliate_id'] );
	$amount   = html_entity_decode( affwp_currency_filter( $args['amount'] ), ENT_COMPAT, 'UTF-8' );

	$message  = sprintf( __( "Congratulations %s!\n\n", "affiliate-wp" ), affiliate_wp()->affiliates->get_affiliate_name( $args['affiliate_id'] ) );
	$message .= sprintf( __( "You have been awarded a new referral of %s on %s!\n\n", "affiliate-wp" ), $amount, home_url() );
	$message .= sprintf( __( "Log into your affiliate area to view your earnings or disable these notifications: %s\n\n", "affiliate-wp" ), affiliate_wp()->login->get_login_url() );
	$message .= "Add your extra line here or modify the above";

	return $message;
}
add_filter( 'affwp_new_referral_email', 'affwp_emails_referral_email', 10, 2 );