Manipulating a single machine is impressive, however the question is how quickly it would be identified by subsequent auditing? How hard would it be to manipula

Manipulating a single machine is impressive, however the question is how quickly it would be identified by subsequent auditing? How hard would it be to manipulate enough machines to sway an election and not get caught? If you have physical access to a single machine then it's not terribly difficult to modify it. Especially if it doesn't meet FIPS140-2. But fooling hundreds of machines and not having the results challenged is absurdly difficult.