Override config per role
As @4k4 commented, I don't think that works.

I'd suggest you either use Page Manager/Panels, which allows to create a page with multiple displays and conditions like based on the user role.

Alternatively, you could create your own controller and return the desired page.

I don't know what you want to do exactly, but yet another option would be to keep two separate pages and redirect authenticated users to the different frontpage. That's similar to how drupal.org works, where you can configure whether your front page should be the default or your dashboard as an authenticated user.