Some, originally offensive, don't change (4)
I believe the answer is:
stet
'don't change' is the definition.
(publishing term)
'some originally offensive' is the wordplay.
'originally' indicates taking the first letters.
'offensive' becomes 'tet' (Tet Offensive, Vietnam War military campaign).
The first letter of 'some' is 's'.
's'+'tet'='STET'
(Other definitions for stet that I've seen before include "Retain this type" , "Let it stand (editing mark)" , "Let it stand (in proofing)" , "'Let it stand, in printing (4)'" , "Notation meaning as is, thus" .)