Just FYI: there is a "Kindlet jailbreak" available, which provides Kindlets with the ability to access all classes (not just the ones whitelisted by amazon), and also allows to read/write files anywhere on the device, use Runtime.exec() etc.
I'm using exactly this for my KT font hack, but I initially developed it for the K3 (so I know it's also working on the K3).
Samples and source code are here: https://www.mobileread.com/forums/sho...d.php?t=163358
Maybe it could be useful
PS: On the K3 the classpath is alphabetically ordered, so you don't even need to replace the original json_simple*.jar. You could simply put the file into /opt/amazon/ebook/lib/ with a name that is "smaller" than json_simple, for instance "jailbreak-backend.jar", or "AAA.jar", or... you get the idea.