A non-home rule municipality shall not assign a “fireman”, as defined in Section 10-3-2, to perform police duties or a “policeman”, as defined in Section 10-3-1, to perform firefighting duties or in any way combine the duties of a fireman or a policeman after his or her appointment from a police department or fire department register of eligibles. A non-home rule municipality shall not administer its fire department’s or police department’s regular work assignments in a manner inconsistent with this Section. This Section does not apply to any municipality that created a department of public safety before January 1, 1998.