Editor, in a way

• Copyreader, e.g
• Bill of Rights writer, e.g.
• Revisionist
• Unexpectedly named by Queen, one changing for the better?
• One improving in the morning, one coming last
• Person who makes change
• One changing a bill
• Constitution modifier, e.g

Wiktionary Word definitions in Wiktionary
n. One who amends.

The Collaborative International Dictionary Word definitions in The Collaborative International Dictionary
Amender \A*mend"er\, n. One who amends.