Allegedly, on or about 17 May 2017, William Mattison sent:
I don't have a LiveUSB, and I get the impression it would take hours to make one.
That all depends...
If you kept an install ISO file somewhere (it doesn't have to be the most recent), you can probably use that to make a live USB from. Otherwise you'd have to download one on some computer, any computer. Depending on what you need to do, there may be smaller ISOs that can have enough tools to do what you need to do.
Writing one of these files to a USB flashdrive can take several minutes. I've had success using the "dd" tool to write the ISO file onto the flashdrive, but there are tools for doing this for you. Some ISOs can't simply be dumped onto the flashdrive, as-is, because they need a different bootblock so the computer will boot from them.