amender; corrector; reviser
A person who makes corrections or amendments, often in formal, editorial, or legislative contexts.
The amender of the bill proposed minor wording changes.
As the corrector of the manuscript, he fixed the typos one by one.
校正者 is a proofreader, focusing on checking printed proofs, whereas 修正者 is a broader term for anyone who makes corrections.
Compound of 修正 (amendment, correction) and 者 (person).