How do you programmatically modify a programmatically created content type?
http://api.drupal.org/api/drupal/modules--field--field.crud.inc/function/field_update_field/7
http://api.drupal.org/api/drupal/modules--field--field.crud.inc/function/field_update_instance/7


Open WWWROOT/profiles/standard/standard.install (starting from line 199)
Profile install creates basic content types (like Article and Basic page)