changeling (n.)

• agent
• alternate
• alternative
• analogy
• backup
• change
• comparison
• copy
• counterfeit
• deputy
• double
• dummy
• equal
• equivalent
• ersatz
• exchange
• fake
• fill-in
• ghost
• ghostwriter
• imitation
• makeshift
• metaphor
• metonymy
• personnel
• phony
• proxy
• relief
• replacement
• representative
• reserves
• ringer
• secondary
• sign
• stand-in
• sub
• substitute
• substitution
• succedaneum
• supplanter
• surrogate
• symbol
• synecdoche
• token
• understudy
• vicar
• vice-regent