Dear Health,
The individual vote do not need to be changed.
Here is how it is/(used to be) done. The troublemaker comes to the polling station early. He disables the opposing candidates. Now, all those who did not want to vote for that candidate can’t. This helps the preferred candidate get a a majority. [There is a feature that is supposed to sound an alarm when the machine is tampered with. It is only useful against a bumbling idiot. Even a below average troublemaker does not shy away from an alarm.] Also, people may start randomly selecting candidates, to see if any of them work. They might keep pushing until they select the only one that works. For this reason, newer machines have the option to clear your choices before you submit the vote. (The older machines are still legal. I do not know why.)