What's the current airplane mode strategy?

After a bit with the Kobo Libra Colour, I've decided to try the Kindle Colorsoft. I *really* like the colors compared to the Kobo, and despite being sluggish compared to my ancient Oasis, it still feels quicker than the Kobo.

That said, what is the current strategy regarding airplane mode so that it doesn't update the firmware? When Amazon allowed files to be downloaded to the computer and transferred through USB, it made sense. How does one add books now and prevents the updates?

Thanks!