this is an old question, and I’m not sure when this was added, but the default values for every field can be set using and acf/load_field filter https://www.advancedcustomfields.com/resources/acfload_field/. The example on this page shows choices, but any field setting can be altered this way, although changing important values like key will cause you problems. To see the settings of any field just output them and you’ll be able to see what you can change.
function my_load_field_filter($field) {
echo '<pre>'; print_r($field); echo '</pre>';
return $field;
}
Hope that helps anyone that’s looking for this type of thing.
