Modified: Generate a "Member Number" for PMPro users at checkout and show it on the PMPro account page.

generate_member_number.php

<?php
/*
	Member Numbers
	
	* Change the generate_member_number function if your member number needs to be in a certain format.
	* Member numbers are generated when users are registered or when the membership account page is accessed for the first time.
*/
//Generate member_number when a user is registered.
function generate_member_number($user_id)
{
	$member_number = get_user_meta($user_id, "member_number", true);
	global $pmpro_pages;// what page are we on
	
	//if no member number, create one
	if(empty($member_number) && is_page($pmpro_pages['checkout']))// only run if going through checkout
		
	//if(empty($member_number))
	{
		global $wpdb;
		
		//this code generates a string 10 characters long of numbers and letters
		while(empty($member_number))
		{
			$scramble = md5(AUTH_KEY . current_time('timestamp') . $user_id . SECURE_AUTH_KEY);
			$member_number = substr($scramble, 0, 10);
			$check = $wpdb->get_var("SELECT meta_value FROM $wpdb->usermeta WHERE meta_value = '" . esc_sql($member_number) . "' LIMIT 1");
			if($check || is_numeric($member_number))
				$member_number = NULL;
		}
		
		//save to user meta
		update_user_meta($user_id, "member_number", $member_number);
		
		return $member_number;
	}
}
add_action('user_register', 'generate_member_number');

//Show it on the membership account page.
function pmpromn_pmpro_account_bullets_bottom()
{
	if(is_user_logged_in())
	{
		global $current_user;
		
		//get member number
		$member_number = get_user_meta($current_user->ID, "member_number", true);
		
		//if no number, generate one
		if(empty($member_number))
			$member_number = generate_member_number($current_user->ID);
		
		//show it
		if(!empty($member_number))
		{
		?>
		<li><strong><?php _e("Member Number", "pmpro");?>:</strong> <?php echo $member_number?></li>
		<?php
		}
	}
}
add_action('pmpro_account_bullets_bottom', 'pmpromn_pmpro_account_bullets_bottom');
add_action('pmpro_invoice_bullets_bottom', 'pmpromn_pmpro_account_bullets_bottom');

//show member_number in confirmation emails
function pmpromn_pmpro_email_filter($email)
{
	global $wpdb;
 	
	//only update admin confirmation emails
	if(strpos($email->template, "checkout") !== false)
	{
		if(!empty($email->data) && !empty($email->data['user_login']))
		{
			$user = get_user_by("login", $email->data['user_login']);			
			if(!empty($user) && !empty($user->ID))
			{
				$member_number = get_user_meta($user->ID, "member_number", true);
				
				if(!empty($member_number))
					$email->body = str_replace("<p>Membership Level", "<p>Member Number:" . $member_number . "</p><p>Membership Level", $email->body);
			}
		}
	}
		
	return $email;
}
add_filter("pmpro_email_filter", "pmpromn_pmpro_email_filter", 30, 2);