Presley to become a convert (9)
I believe the answer is:
proselyte
'a convert' is the definition.
(term for a religious convert)
'presley to become' is the wordplay.
'become' indicates an anagram.
'presley'+'to'='presleyto'
'presleyto' with letters rearranged gives 'PROSELYTE'.
(Other definitions for proselyte that I've seen before include "One now thinks differently" , "Convert to a religion, particularly Jewish" , "recruit" , "Religious convert" .)