How do I completely disable user profiles and the dedicated login page in Drupal 7?
Yes, you can change built in menu / page callbacks with hook_menu_alter

For example, alter user_menu

/**
 * Implements hook_menu_alter
 */
function MYMODULE_menu_alter(&amp;$items){
  // Go to front page when visiting /user and /user/login
  $items['user']['page callback'] = 'drupal_goto';
}