Key changes made in the UPSC examination structure in the last decade include the introduction of the optional subject format in Mains, revised General Studies papers, and the inclusion of an emphasis on ethics in the syllabus. The preliminary exam was revamped to focus more on current affairs and logical reasoning. Besides, the weightage of marks for interview assessments has been adjusted to ensure a balanced evaluation across all stages. Lastly, the negative marking system was formalized to deter guessing, streamlining the examination process overall.