Referred to a change of diet for Charlie (5)
I believe the answer is:
cited
'referred to' is the definition.
('cite' can be a synonym of 'refer to')
'a change of diet for charlie' is the wordplay.
'a change of' indicates an anagram (the letter order is changed).
'for' is a charade indicator (letters next to each other) (I've seen this in other clues).
'charlie' becomes 'C' (phonetic alphabet).
'diet' with letters rearranged gives 'ited'.
'ited' after 'c' is 'CITED'.
(Other definitions for cited that I've seen before include "Commended" , "Made reference to -- edict (anag)" , "Summoned" , "Called for" , "Quoted or mentioned as example" .)