How much could a modern electronic-warfare ship change the Napoleonic Wars?
Short answerAlmost nothing, because there are no radio communications to attack; the capability only begins to matter around the Russo-Japanese War and First World War.
NotesA modern electronic-warfare ship sent to the Napoleonic Wars would find no radio network to intercept, jam, or exploit. Its specialized mission therefore contributes almost nothing to the communications system of that era. The Russo-Japanese War is the earliest plausible setting in which the capability starts to matter. The First World War offers a much stronger target environment, while the dense electronic systems of the Second World War would finally let the ship use its role fully.