Changes to an organization's overall structure, such as creating a new company or restructuring how organizations relate to one another within a hierarchy, affect historical reporting, security, and financial data, and therefore require a controlled, effective-dated mechanism to implement properly. The Official Workday Pro Procure-to-Pay Guide describes the reorganization event as the required mechanism for creating a company or making structural changes to an organization hierarchy, ensuring that the change is properly effective-dated, documented, and that dependent data, such as worker assignments and reporting relationships, is updated consistently. Option A is incorrect because custom worktags are reporting dimensions used for tagging transactions and do not themselves capture or implement organizational structure changes. Option B is incorrect because, while transactional changes to cost centers may route through business processes, the question concerns structural changes to the organization hierarchy itself, which specifically requires a reorganization event. Option D is incorrect because reassigning workers to appropriate sub-types is typically a consequence that occurs as part of, or following, a reorganization event, not the mechanism that creates the structural change itself.