I do a lot of review stuff lately. Sometimes I reject suggested edits, because the editor makes changes in the source code (I'm not talking typos) or adds whole parts of explanation.
In such a case I leave a custom message like:
Please add this as a comment, that the user can update his question/answer.
But I wonder whether this is read by the user or is it likely to go under? Is this prominent? Is it displayed in the inbox from the StackExchange menu?
In my profile I can find it under "activity/suggestions" but I don't think that I got any notification about it. I'm only aware because I think that some suggestions might get lost that way.
invalid edit
applies, as that is used to say the edit is replying to the post (and therefore should be a comment).