And doing that on any kind of scale will undoubtedly end with the perpetrator in jail for voter fraud. It's easy to speculate about how, it's a lot harder to do it in a way that gets away with it without leaving a trail that eventually catches up with them.
Yes and no. I would argue that if enough people are doing this on a small scale then there's potential for significant impact.
All that is required is the belief that it is imperative your team wins. The ideology that you can be dishonest if you do it for the right reasons grants considerable latitude for these types of corrections.
In the case you present, one bad actor is somehow able to manipulate the system en mass. That is certainly likely to draw attention, as you've pointed out.
And if the fraud is big enough the election in that polling station will be repeated. The more polling stations you have, the harder it is that a single station can impact overall results.
