Changing clothes, a chore for mistress? (13)
I believe the answer is:
schoolteacher
'mistress?' is the definition.
(schoolmistress)
'changing clothes a chore' is the wordplay.
'changing' is an anagram indicator.
'clothes'+'a'+'chore'='clothesachore'
'clothesachore' is an anagram of 'SCHOOLTEACHER'.
'for' acts as a link.
(Other definitions for schoolteacher that I've seen before include "tutor" , "Educator" , "Instructor" , "Master, say" , "Chips perhaps" .)