That may happen in some places, but not where I work the polls. The four poll workers are required to be two from each major party. Even if we or they wanted to do so, we could not vote for other individuals without the other side's cooperation.
That's not to say that some RAT poll workers wouldn't register Republican to get an all RAT crew in some precincts. But they'd probably have to wait until after the polls closed to do their dirty deed, and the machines time stamp everything.
Some still takes place at the precinct level nowadays , especially in big cities with minority majorities, with the traditional church van visiting 10-12 precincts. You report early to the church hall, get a hearty breakfast, $20-30 in street money, make sure your absentee ballots are in order, then you hit the polls. It's tradition. If the church is well organized, you'll get some lunch, too, and maybe another trip round the precincts. Sometimes the street money is paid for each voting receipt. 10-12 not unheard of. Republican poll workers? In some hell-hole like Philadelphia? ROTFLMAO!
But these days, the major chicanery is done with absentees and computers. Dead people are absent, are they not? Virtual people invented by your Sim City program are absent, too. Are they not? Virtual voters are often generated from the dead, who are presumed to have multi-generational families.
These techniques grew up with computers. The pioneers were the Sanchez Sisters in Orange county, CA. Loretta's team just plain invented about 7500 voters. They also worked hard to illegally register aliens, legal and illegal, felons. The tech has matured to the point where CA is reputed to have half-a-million fraudulent votes available. It has also been reported that about 75 seats in the CA legislature were filled by fraudulent election tactics.
Judges of Elections know the tricks. 75 voters registered at a house that doesn't exist on a non-existent street; another 50 registered at an address that is a gas station ... or an empty lot.
6100 dead voted in one county ? ... that's more than enough to throw an election. In local elections where 15% turnout is considered good ... like schoolboard ... 10 fraudulent absentee votes can throw the results.
Happens all the time in Chicago. Not enough Pubbies to man the polls and you have to vote for the party you work for. So I saw real Dems get a pubbie balllot and cast it blank. One poll worker thought I was one of these so he began to tell me all the ways to cheat the system. It was quite an eye opener for a young seminary student. This was the next precinct over from where Bammy voted in Hyde Park.