substitutor
/ˈsʌbstɪtjuːtə/ /ˈsʌbstɪtʃuːtə/noun
A person who puts one thing in place of another; a person who replaces one thing with another; specifically a person who sells an inferior or cheaper product (originally a medicine) in place of the one desired by the purchaser, with the aim of increasing profit; a person who passes off one manufacturer's goods as another's.
Origin
Early 17th century (in an earlier sense). Partly from post-classical Latin substitutor person who appoints a substitute, and partly from substitute + -or.