Depends on the terminal I think. Pretty sure KDE's Konsole warns you that commands may be run when pasting something with newlines, but still allows it.
There is an exploit which addresses copy pasting things in terminal. Where you'd copy one thing, but when pasting you get more than you bargained for. Any decent terminal would ignore \n for this reason or at least not treat it as pressing enter.
Well they did have the type the command, and to do that they would first have to navigate to the terminal (assuming the machine isn't running just a plain tty) first.
