Remind me of how a programmer fixed lottery games:
https://www.cnbc.com/2017/06/30/mastermind-of-lottery-fraud-admits-he-rigged-jackpots.html
...Investigators say Tipton installed code that let the computers work as should on all but three days of the year — May 27, Nov. 22 and Dec. 29 — when they would produce predictable numbers if the drawings occurred on Wednesdays or Saturdays after 8 p.m...
Yea, that would be part of it too. Only have the hacked code execute on the evening of Election Day. That way all the pre and post testing would show up fine.
Now if they use optical scanners, it is always possible to later compare sample scanner readings with sample hand counts (which should always be done for a contested election), and if they differ, then hand-count everything (and jail the Leftist who hacked in). But the key is the paper...no one that I know of has figured out a way to change what is written on paper.