Implements hook_custom_block_update().
function custom_block_test_custom_block_update(CustomBlock $custom_block) {
// Determine changes on update.
if (!empty($custom_block->original) && $custom_block->original->info->value == 'test_changes') {
if ($custom_block->original->info->value != $custom_block->info->value) {
$custom_block->info->value .= '_update';
}
}
}