It is hopeless to hook into the image-edit.php ajax loaded screen. This issue, to pre-select “thumbnail only” radio option instead of “all images” can be solved by jQuery. The snippet in your functions.php can be improved, but works:
// Populate thumbnail settings
function entex_admin_image_editor_activate_tweaks() {
?>
<script type="text/javascript">
jQuery(document).ready(function($) {
$(document).ajaxStop(function(){
if($('.imgedit-settings input[value="thumbnail"]').get(0)) {
$el = $('.imgedit-settings input[value="thumbnail"]');
if($el.data('manipulated')) return;
$el.data('manipulated', true);
$el.prop('checked', true).parent().siblings().find('input').prop('checked', false);
}
});
});
</script>
<?php
}
function entex_admin_image_editor_current_screen($screen){
if($screen->base != 'post' || $screen->post_type != 'attachment') return;
add_action('admin_footer', 'entex_admin_image_editor_activate_tweaks');
}
add_action('current_screen', 'entex_admin_image_editor_current_screen');