Is it permissible for guards to agree to one guard's rotating shift instead of two at night, knowing that the nature of the work allows for it and the area is safe?

It is not permissible to violate the terms of the contract, work timings, or work procedures, in compliance with Allah's saying: "O you who have believed, fulfill [all] contracts," and "Do not betray Allah and the Messenger or betray your trusts while you know." And according to the Prophet, peace and blessings be upon him, "Muslims are bound by their conditions." The security afforded by the workplace does not justify violating the terms, and the knowledge of the management about such violations might lead to the dismissal of some workers.