This mutator adds the possibility of having twelve cameras in the No Mercy heist when there are four human players at the start of the heist and the random chance of Bain not knowing if there are twelve or nine cameras. It includes special unused dialogues for said situations although there is no reference for any of them in the original mission script code, so don't consider this a "restoration" since we don't know exactly how the "unknown cameras" situation would originally have worked.
The mutator is only available on overkill and above and requires a full lobby to take effect.