Priest perhaps forces son to change (9)
I believe the answer is:
confessor
'priest' is the definition.
(I know that confessor is a type of priest)
'forces son to change' is the wordplay.
'to change' is an anagram indicator.
'forces'+'son'='forcesson'
'forcesson' with letters rearranged gives 'CONFESSOR'.
'perhaps' acts as a link.
(Other definitions for confessor that I've seen before include "One who makes a declaration of faith" , "Priest who hears sins" , "One who admits to sins" , "Edward, for example?" , "One listens to the sins of others" .)