THESAURUS
substitute for
act for, answer for, appear for, back up, change places with, commission, crowd out, cut out, deputize, displace, double for, fill in for, front for, ghost, ghostwrite, pinch-hit, pinch-hit for, relieve, replace, represent, speak for, spell, spell off, stand in for, subrogate, succeed, supersede, supplant, swap places with, understudy, understudy for