AffiliateWP - Remove the affiliate_referral_url shortcode and add the same shortcode back which returns the affiliate referral URL in a site.com/ref/username format

gistfile1.php

<?php

// remove original shortcode
remove_shortcode( 'affiliate_referral_url' );

/**
 * Add our new shortcode which returns the affiliate referral URL in a site.com/ref/username format
 */
function affwp_custom_referral_url_shortcode( $atts, $content = null ) {

	if ( ! affwp_is_affiliate() ) {
		return;
	}

	shortcode_atts( array(
		'url' => ''
	), $atts, 'affiliate_referral_url' );

	if ( ! empty( $content ) ) {
		$base = $content;
	} else {
		$base = ! empty( $atts[ 'url' ] ) ? $atts[ 'url' ] : home_url( '/' );
	}

	$affiliate = affwp_get_affiliate( affwp_get_affiliate_id() );
	$user_info = get_userdata( $affiliate->user_id );
	$username  = esc_html( $user_info->user_login );

	return $base . affiliate_wp()->tracking->get_referral_var() . '/' . $username;
}
add_shortcode( 'affiliate_referral_url', 'affwp_custom_referral_url_shortcode' );