From a previous software update:
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.