Hi @jepser
You are very close, but looking at the /js/input/ajax.js file, you can see that the acf.screen objecrt needs to be updated with the new value!
Here is an example of the page template
$(document).on('change', '#page_template', function(){
acf.screen.page_template = $(this).val();
$(document).trigger('acf/update_field_groups');
});
You should be able to see how to change page_template to post_template!
Thanks
E