Set a default theme and an admin theme during profile installation

profile.install

<?php

/**
 * Implements hook_install().
 */
function my_custom_profile_install() {

  // Here, the admin theme is adminimal, and the default theme is called bueno
  // It seems like if the themes are not enabled in the database directly, just setting the default theme does not work.

  // Enable the admin theme.
  db_update('system')->fields(array('status' => 1))->condition('type', 'theme')->condition('name', 'adminimal')->execute();
  // Enable Bueno
  db_update('system')->fields(array('status' => 1))->condition('type', 'theme')->condition('name', 'bueno')->execute();
  theme_disable(array('bartik'));

  // Set the admin theme and enable it 
  variable_set('admin_theme', 'adminimal');
  variable_set('node_admin_theme', '1');
  // Set the default theme
  variable_set('theme_default', 'bueno');
}