This writer changed - less a complaint (7)
I believe the answer is:
measles
'complaint' is the definition.
(measles is a kind of health problem)
'this writer changed less a' is the wordplay.
'this writer' becomes 'me' (the person who wrote the clues).
'changed' indicates an anagram.
'less'+'a'='lessa'
'lessa' is an anagram of 'asles'.
'me'+'asles'='MEASLES'
(Other definitions for measles that I've seen before include "Spotty viral infection" , "An infectious fever" , "Disease where spots may be seen" , "Viral disease once common in children" , "Viral disease with rash" .)