Pity has transformed yours truly (5)
I believe the answer is:
shame
'pity' is the definition.
(I know that pity can be written as shame)
'has transformed yours truly' is the wordplay.
'transformed' indicates an anagram.
'yours truly' becomes 'me' (the person who set this crossword).
'has' anagrammed gives 'sha'.
'sha'+'me'='SHAME'
(Other definitions for shame that I've seen before include "Disgrace - Salman Rushdie novel" , "Painful emotion resulting from guilt" , "disgraceful" , "scandal" , "pity!" .)