Yeah definitely. My layperson's understanding of the overall security measures suggests that it is though. Drives are loaded to machines with multiple witnesses signing off on the serial numbers of each, machines are kept in a secure location once loaded, drives are removed with multiple witnesses and SN checked before putting them together in a tamper resistent bag. If someone did defeat all of that and gain access to a drive (or multiple) they're encrypted. If they beat the encryption the drives are formatted to the proprietary file system that voting machine company has built which the attacker would either need a machine that runs, or have the ability to emulate that environment to be able to access the data on the drives....which my knowledge breaks down at this point, but I'd imagine they would have be able to not just alter the data, but do it in a way that doesn't log the results of the change, while doing it in a proprietary OS built to not allow that to happen.
and they would have to do all of that in between the time the drives were removed, and roughly when they were expected to arrive at the central registry that they were doing the vote tallying at.
And with all of that said....if we were going to see that type of election attack, you would think that the amount of hand counted recounts we've seen over the last ~20 years would have uncovered just one attempt to do this and we haven't. Because it's fucking hard and there are better/easier ways to influence an election.