Support for Drupal 7 is ending on 5 January 2025—it’s time to migrate to Drupal 10! Learn about the many benefits of Drupal 10 and find migration tools in our resource center.
Overwriting configuration in Drupal 8 from a theme is not possible during the install process, only profiles can do that. However, you can use DrupalConsole to override some configuration without no problems. For this reason, you can use the following commands to override some configuration need it.
Currently themes in Drupal 8 does not support hook_uninstall, for this reason if you are trying to reinstall Casper you will run into this issue https://www.drupal.org/node/2660764. Where you cannot install the theme again because of that error.