Surprisingly simple way to import fields into ACF GUI from PHP code

acf-import-from-php.php

<?php

// To re-import ACF settings from acf_add_local_field_group() into the ACF wp-admin GUI

$group_key = 'group_111222333';  // This must match the key as defined at the top of acf_add_local_field_group()

//After the field group is completely set up, get the field group.
$group = acf_get_field_group($group_key);

// then get the fields for the group
$group['fields'] = acf_get_fields($group_key);

// output JSON for saving into a file
echo(json_encode($group));
die();
/*
// or  write the field group to a file
$filename = '/path/to/your/file.json'
$handle = fopen($file, 'w');
fwrite($handle, json_encode($group));
fclose($handle);
*/