Agreements deviating from section 152 (1) to (4), and sections 153 to 155, as well as sections 157, 158, 161 and sections 163 to 170, to the detriment of the policyholder, the insured person, or the person entitled to subrogation, are not permitted. Agreement may be reached to the effect that the policyholder’s request for conversion in accordance with section 165, and his or her termination of the contract in accordance with section 168, must be made in writing.