Constitution modifier, e.g

• Copyreader, e.g.
• Change maker
• Person who makes change
• Maker of a change or revision
• Unexpectedly named by Queen, one changing for the better?
• Bill modifier, e.g
• Editor, in a way
• Revisionist

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

Wiktionary Word definitions in Wiktionary
n. One who amends.