With respect to any matters pertaining to the making of rates or rating systems, two or more admitted insurers having a common ownership or operating in this State under common management or control, are hereby authorized to act in concert between or among themselves the same as if they constituted a single insurer. For any coverage for a policy for automobile and any other form of insurance subject to this chapter issued or renewed on or after November 8, 1988, every insurer shall reduce its charges to levels which are at least 20% less than the charges for the same coverage which were in effect on November 8, 1987. Commencing November 8, 1989, insurance rates subject to this chapter must be approved by the commissioner prior to their use.