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

(2) Effective January 1, 1990, except for riders or endorsements issued to bring a policy into compliance with changes to the minimum benefit standards or other contractual benefits required by this chapter or as amended:

(a) An amendment to a medicare supplement insurance policy or certificate that increases the premium must be requested or accepted by the policyholder in writing; and

(b) Where separate additional premium is charged for a rider, endorsement or other amendment to the contractual benefits of a medicare supplement insurance policy or certificate, the premium charged must be set forth in the policy.