Changes that alter the scope, schedule, cost, or deliverables of the contract require formal contract modifications. Introducing new regulatory requirements (C) changes the scope and obligations, and replacing material types (E) can alter the quality and specifications, thus affecting contractual terms.
According to the PMBOK Guide - Seventh Edition (Governance Domain and Procurement Performance Domain), any scope-affecting changes must go through change control and may trigger contract revisions.
Option A (change control team) affects internal governance, not the vendor's contractual scope.
Option B (adding vendors) may affect resource flexibility but not specific contract obligations with an existing vendor.
Option D (vendor name change due to acquisition) is administrative and does not usually trigger a change in obligations.
Reference:
PMBOK Guide - Seventh Edition, Procurement and Governance Domains
PMI's Practice Standard for Project Contracts