@Kasrielle
There was an easy way to block the execution of updates on a Kindle (PW1) reported some time ago:
https://www.mobileread.com/forums/sho...d.php?t=219986 - that worked on non-jailbroken devices iirc.
In short: create an empty folder named "update.bin.tmp.partial" (without the quotes) in the root directory - updates will be downloaded but not executed. Does it work on latest firmwares and/or on newer devices than a PW1? I don't know and can't test it.
All credits to richy1989