Default some PMPro fields based on other user meta.

get_user_metadata_pmpro_prepop.php

<?php // copy from below
/**
 * Synchronize WooCommerce Billing Address and PMPro Billing Address
 * 
 * You can add this recipe to your site by creating a custom plugin
 * or using the Code Snippets plugin available for free in the WordPress repository.
 * Read this companion article for step-by-step directions on either method.
 * https://www.paidmembershipspro.com/create-a-plugin-for-pmpro-customizations/
 */
function get_user_metadata_pmpro_prepop($value, $user_id, $meta_key, $single) {	
	//fields to sync, make sure there are no loops in this
	$sync_fields = array(
		"pmpro_bfirstname" => "billing_first_name",
		"pmpro_blastname" => "billing_last_name",
		"pmpro_baddress1" => "billing_address_1",
		"pmpro_baddress2" => "billing_address_2",
		"pmpro_bcity" => "billing_city",
		"pmpro_bstate" => "billing_state",
		"pmpro_bzipcode" => "billing_postcode",
		"pmpro_bcountry" => "billing_country",
		"pmpro_bphone" => "billing_phone",
	);
	
	//is this a field we try to sync?
	if(!empty($sync_fields[$meta_key])) {
		//get the actual meta field
		$meta_cache = wp_cache_get($user_id, 'user_meta');
		if ( !$meta_cache ) {
			$meta_cache = update_meta_cache( 'user', array( $user_id ) );
			$meta_cache = $meta_cache[$user_id];
		}
		
		//only lookup the other value if the meta field is empty
		if(empty($meta_cache[$meta_key])) {
			$value = get_user_meta($user_id, $sync_fields[$meta_key], $single);
		}
	}

	return $value;
}
add_filter('get_user_metadata', 'get_user_metadata_pmpro_prepop', 10, 4);