https://www.jpl.nasa.gov/news/nasas-voyager-team-focuses-on-...
> Because of the spacecraft’s age and the communication lag time, there’s some risk the patch could overwrite essential code or have other unintended effects on the spacecraft. To reduce those risks, the team has spent months writing, reviewing, and checking the code. As an added safety precaution, Voyager 2 will receive the patch first and serve as a testbed for its twin. Voyager 1 is farther from Earth than any other spacecraft, making its data more valuable.
> The team will upload the patch and do a readout of the AACS memory to make sure it’s in the right place on Friday, Oct. 20. If no immediate issues arise, the team will issue a command on Saturday, Oct. 28, to see if the patch is operating as it should.
https://www.businessinsider.com/engineers-turn-to-voyager-de...
> During the first 12 years of the Voyager mission, thousands of engineers worked on the project, Dodd said. "As they retired in the '70s and '80s, there wasn't a big push to have a project document library. People would take their boxes home to their garage," Dodd added. In modern missions, NASA keeps more robust records of documentation.
Nowadays we've learned to make a duplicate.
https://www.jpl.nasa.gov/news/nasa-readies-perseverance-mars...
Back when the Spirit rover got trapped, they used its twin to pre-game possible approaches in similar soil.
https://www.jpl.nasa.gov/news/mars-and-earth-activities-aim-...
Given the tiny amount of storage, there's presumably no scope for rolling back changes after an error, so are they at risk of bricking the spacecraft every time the flight engineers (and just for once, I think the term "software engineer" is truly justified) make a change?