Assigns a random 6 digit number for a username automatically. Two variations...the first will show the username field with number already filled, but editing is disabled. The second variations (uncomment the lines) will not show the username field at all, but will simply generate the numerical username and display it on the confirmation page.

pmpro-assign-username-at-checkout.php

/*
Assigns a random 6 digit number for a username automatically.
Two variations...
	the first will show the username field with number already filled, but editing is disabled.
	The second variations (uncomment the lines) will not show the username field at all, but will simply generate the numerical username and display it on the confirmation page.
*/

function my_pmpro_checkout_after_user_fields()
{
	echo "<script>";
//	echo "jQuery('#username').hide();";
//	echo "jQuery('label[for=username]').hide();";
	
	
	if(empty($_REQUEST['submit-checkout']))
	{
		echo
		"//Taken from: https://stackoverflow.com/questions/1527803/generating-random-whole-numbers-in-javascript-in-a-specific-range
		function getRandomInt(min, max) {
			return Math.floor(Math.random() * (max - min + 1)) + min;
		}

		var rand_num_username;
		rand_num_username = getRandomInt(100000, 999999);
		jQuery('#username').val(rand_num_username);
		jQuery('#username').prop('readonly', true);";
	}
	echo "</script>";
	
}
add_action('pmpro_checkout_after_user_fields', 'my_pmpro_checkout_after_user_fields');

function my_pmpro_required_user_fields($pmpro_required_user_fields)
{
	unset($pmpro_required_user_fields['username']);
	return $pmpro_required_user_fields;
}

//add_filter('pmpro_required_user_fields', 'my_pmpro_required_user_fields');

Can I use a variation of this to assign the sponsoring user's email to the sponsored user? (Note: I've already used Allow Multiple Plugins to let multiple users use the same email address).

function parent_email_add()
{
global $wpdb, $pmpro_level, $discount_code;

if($pmpro_level->id == 5 && !empty($discount_code)) // 5 is the sponsoring level
{
$code_id = $wpdb->get_var( "SELECT * FROM $wpdb->pmpro_discount_codes WHERE code = '" . esc_sql( $discount_code ) . "' LIMIT 1" ); //finds ID for sponsored code
$code_user_ids = get_option("pmpro_code_user_ids"); //searches database of discount codes
$parent_id = $code_user_ids[$code_id]; // finds user ID associated with sponsored code
$parent = get_user_by('id', $parent_id);
$parent_email = $parent->user_email; // get parent email
if(empty($_REQUEST['submit-checkout']))
{
echo " <script> jQuery('#bemail').val($parent_email); </script>";
}
}
}

add_action ("pmpro_checkout_after_user_fields", "parent_email_add", 10, 4);

function my_pmpro_required_user_fields($pmpro_required_user_fields)
{
unset($pmpro_required_user_fields['bemail']);
return $pmpro_required_user_fields;
}