Context: Software systems in regulated domains must continually adapt to legal changes, yet practitioners often handle updates manually with limited support, making compliance work costly and error prone. Recent advances in LLMs prompt the question of how automation can reliably assist this process.

Objectives: We aim to (1) characterize the nature of regulatory changes and derive a systematic taxonomy, (2) understand through the lens of practitioners where automation is most useful, and (3) assess the feasibility of using LLMs for detecting and classifying regulatory changes.

Method: We conducted a mixed-methods study grounded in the German social security (DEÜV) in collaboration with practitioners from a FinTech company. First, we developed a taxonomy of regulatory changes through manual document analysis of four Regulatory Implementation Specifications (RIS), followed by a workshop and expert interviews. Second, we validated the taxonomy and elicited challenges through semi-structured practitioner interviews. Third, we built a gold-standard dataset of 93 annotated change instances and evaluated seven state-of-the-art LLMs within an automated detection and classification pipeline.

Results: The taxonomy defines five change scopes and four optional context dimensions. Practitioners found it intuitive and useful for filtering relevant changes, particularly Data and Field updates, but reported challenges such as tight deadlines, legal ambiguity, limited traceability, and overlapping categories. In automation, proprietary LLMs performed best, while performance dropped on narrative or weakly structured documents, highlighting sensitivity to document format.

Conclusion: The proposed taxonomy provides a practical lens for organizing regulatory change information, and LLMs can support the identification and classification of recurring, structurally explicit changes. Their limitations on context-dependent and infrequent categories suggest that automation should complement, rather than replace, expert assessment, motivating future work on human-in-the-loop compliance tooling across broader regulatory ecosystems.