When creating a content type programmatically, is there a way to disable promoting to the front page by default?
Whether nodes of a particular content type are promoted to the front page by default is stored in the Drupal array variable node_options_{content type name}:

$node_options = variable_get('node_options_{content type name}', array());
$promote_key = array_search('promote', $node_options);
if ($promote_key !== false) {
  unset($node_options[$promote_key]);
  variable_set('node_options_{content type name}', $node_options);
}