BuddyPress.org

I figured this out by cobbling together some code. Just copy this into a new .php file, upload to /plugins and activate. You’ll need to change ‘Referrer’ to whatever profile field you have instead.

<?php
/*
Plugin Name: Custom New User Email
Description: Changes the copy in the email sent out to new users
*/
 
// Redefine user notification function
if ( !function_exists('wp_new_user_notification') ) {
    function wp_new_user_notification( $user_id, $plaintext_pass = '' ) {
        $user = get_userdata( $user_id );
      
	// The blogname option is escaped with esc_html on the way into the database in sanitize_option
	// we want to reverse this for the plain text arena of emails.
	$blogname = wp_specialchars_decode(get_option('blogname'), ENT_QUOTES);
	
	// find the profile field for referrer
	$field1 = xprofile_get_field_data( 'Referrer', $user_id );

	$message  = sprintf(__('New user registration on your site %s:'), $blogname) . "\r\n\r\n";
	$message .= sprintf(__('Username: %s'), $user->user_login) . "\r\n\r\n";
	$message .= sprintf(__('E-mail: %s'), $user->user_email) . "\r\n\r\n";
	$message .= sprintf(__('Referrer: %s'), $field1) . "\r\n";

	@wp_mail(get_option('admin_email'), sprintf(__('[%s] New User Registration'), $blogname), $message);

	if ( empty($plaintext_pass) )
		return;

	$message  = sprintf(__('Username: %s'), $user->user_login) . "\r\n";
	$message .= sprintf(__('Password: %s'), $plaintext_pass) . "\r\n";
	$message .= wp_login_url() . "\r\n";

	wp_mail($user->user_email, sprintf(__('[%s] Your username and password'), $blogname), $message);
 
     }
}
 
?>