Over time, laws change to meet evolving social needs. Requirements engineers that develop software for regulated domains, such as healthcare or finance, must adapt their software as laws change to maintain legal compliance. In the United States, regulatory agencies will almost always release a proposed regulation, or rule, and accept comments from the public. The agency then considers these comments when drafting a final rule that will be binding on the regulated domain. Herein, we examine how these proposed rules evolve into final rules, and propose an Adaptability Framework. This framework can aid software engineers in predicting what areas of a proposed rule are most likely to evolve, allowing engineers to begin building towards the more stable sections of the rule. We develop the framework through a formative study using the Health Insurance Portability and Accountability (HIPAA) Security Rule and apply it in a summative study on the Health Information Technology: Initial Set of Standards, Implementation Specifications, and Certification Criteria for Electronic Health Record Technology.