If a client wants to customize a specific page (route) that already exists, DO NOT edit the file in ClientUI\app\plugins\core\admin\{{theRouteFileName}}.tsx. Instead, create a file in ClientUI\app\routes\{{theRouteFileName+override}}.tsx. For example, if you want to override ClientUI\app\plugins\core\admin\admin.settings.theme.route.tsx, create a file here: ClientUI\app\routes\admin.settings.theme.route.override.tsx.