Obviously not an official response… but looking at things from a computation standpoint:
When you send in your 72 hour job, it is processed by the cloud computers before you ever press the Start button. That processing turns it into a waveform which will control your machine.
If, while your 72 hour job is running, Glowforge attempts to change things, they are changing either the Cloud side, or the Machine side.
Cloud side changes: The change would be in how the computation happens, which is already done for yours. So this has no bearing on your job. It is possible there is a change to communication protocols, that would have an effect on your job… but I would expect that such a change would be exceedingly rare (especially since it would have to go hand in hand with a firmware adjustment)
Machine side changes: The changes would be to Firmware, as that is the only thing on the machine. Here you could have issues, but only if they set up the update to ignore all current functions, which would be a very odd case. It should instead be obvious to the system that the machine is currently communicating with the cloud, and it waits to download, or at least that the machine is in use, and it waits to flash. But… here it would be possible things mess up. But… firmware adjustments are hopefully few and far between.