(1) In order to assure the orderly implementation and conversion of medicare supplement insurance benefits due to changes in the federal medicare program and to eliminate provisions which may duplicate medicare:

(a) No later than January 1, 1990, all insurers must substitute new policies for all medicare supplement insurance policies or contracts sold to residents of this state prior to January 1, 1990, where policies were amended by riders or endorsements to comply with changes to medicare.

(b) Effective January 1, 1990, subject to RCW 48.66.050(2), and except for riders or endorsements issued in accordance with subsection (2) of this section, no rider, endorsement, waiver, or any other means of contractual modification may be used by an insurer to exclude, limit, or reduce the coverage or benefits of a medicare supplement insurance policy issued to a resident of this state.

(2)(a) Effective January 1, 1990, only riders or endorsements which increase benefits or coverage may be used in this state.

(b) A medicare supplement insurance policy amendment which increases the premium must be requested or accepted by the insured in writing.

(c) Where separate additional premium is charged for a medicare supplement insurance policy rider, endorsement or other amendment thereto, such premium charge shall be set forth in the policy.