I'm writing an installation profile and want to switch default system theme (Garland) to my own theme. The theme should replace Garland on the first step - when I choose installation profile. On this stage Drupal is not bootstrapped, so I can not set appropriate DB variables.
Any ideas how to do that?
Short answer, you can't. It's fairly hard-coded in _drupal_maintenance_theme():
// Install and update pages are treated differently to prevent theming overrides.
if (defined('MAINTENANCE_MODE') && (MAINTENANCE_MODE == 'install' || MAINTENANCE_MODE == 'update')) {
$theme = 'minnelli';
}