When I changed by MINI, I had the HU transferred from the old MC
to the new one by the dealer. When I came to change the HU later, I found that the dealer had screwed the HU into the cradle in a similar way to the OEM HU. I only found this after spending ages trying to remove the HU with the removal keys.
Just follow the instructions in the FAQ to remove the OEM HU, and once you have the dash pillars removed you'll see if someone has used screws.