Editing letters set on fire (7)
I believe the answer is:
ignited
'set on fire' is the definition.
(I've seen this before)
'editing letters' is the wordplay.
'letters' is an anagram indicator.
'editing' is an anagram of 'IGNITED'.
(Other definitions for ignited that I've seen before include "Gin diet (anag.)" , "Set on fire" , "Set alight" , "Sparked off" , "Caught fire" .)