Yes, you can hack the machines with physical access.

It would require on some physically hooking a computer up and on others actually taking the machine apart and swapping chips or birds of chips.

Now, let's look at what that would require.

Voting machines are stored all over in county board of elections offices, in facilities with alarms.

To hack them you would have to break in to the office, remove the machines from storage, take them apart one at a time and swap parts or boot each one up and run upgrades, test them all to make sure it took and you didn't kill the machines, power them back down, put them back in storage, leave no trace you were there and then get away without being caught.

Now, that's time consuming. And risky. It's. It easy to pull that off once without either getting caught or somebody noticing you were there.

It would be hard enough to pull off with one location. To pull it off in enough scale to actually change the election outcome would require it be done thousands of times over and over at different counties. All without not once being caught or leaving any trace you were there.

That's the stuff of movies and novels. The odds of that being pulled off in reality are astronomically low.

And even if they managed to do all that, how are they writing a code that is undetectable in all the pre-election testing and validation and post-Election auditing?