This edit suggestion made by user A takes (reasonable-seeming code) suggested by user B and applies it to an answer by user C.
- Reject the edit on the grounds that user C should make the edit only if he/she feels it is appropraite?
- Approve the edit on the grounds that this looks like a good suggestion?
- Only approve the edit if I have domain knowledge and know that this improves the answer, and ignore the edit otherwise?
In general, when is it acceptable for one user to edit another user's answer in a non-trivial way?