Auto generate passwords with Paid Memberships Pro

pmpro-auto-password-generation.php

/*
  Automatically generate password on checkout page.
  
  Note: if you want to remove the entire user area and generate usernames and passwords, simply set the pmpro_skip_account_fields filter to return false.
	
	Use the intstructions here (http://www.paidmembershipspro.com/documentation/advanced-techniques/templates/) to add a checkout page template with the password fields removed.
	
	Uncheck the "Default WP notification email. (Recommended: Leave unchecked. Members will still get an email confirmation from PMPro after checkout.)" option in the PMPro Emails Settings tab.
*/
function my_generate_passwords()
{
	if(!empty($_REQUEST['username']) && empty($_REQUEST['password']))
	{
		$_REQUEST['password'] = pmpro_getDiscountCode() . pmpro_getDiscountCode();	//using two random discount codes
		$_REQUEST['password2'] = $_REQUEST['password'];
	}
}
add_action("init", "my_generate_passwords");

What would be the correct way to set pmpro_skip_account_fields to false? The following didn't seem to work:

$skip_account_fields = apply_filters("pmpro_skip_account_fields", "false");

When the filter is set to false, is the Username that is automatically generated random? Or is the signup email used?

Where am I supposed to place this code? in the checkout.php template or someplace else?

Please can you let me know how I can add this as I put it in the pmpro-customizations plugin but it doesn't reflect on the front-end?