The term that accurately describes a document that modifies the original wording of an insurance policy is an endorsement. An endorsement is typically used to add or change coverage, clarify terms, or make other adjustments to the policy conditions. This is a standard practice in the insurance industry, allowing policies to be tailored to meet the specific needs of the policyholder without having to completely rewrite the original contract.
Other terms, like appendix, addendum, and amendment, generally refer to supplementary or additional materials or changes in different contexts but do not specifically denote modifications to the wording of an insurance policy in the way endorsements do. An appendix might be used to provide additional information or context, while an addendum usually is seen in contractual situations to provide more detail or additional provisions. An amendment may refer to a broader change but is not commonly used specifically for insurance policies in the same precise manner as endorsement.