1st try to recover:
- I've canceled the fake registration
Now I could say I have all that I've need: homescreen deactivated, an unregistered Kindle, the last fw and, a useful function - I can read my books on it
But why so?
I've re-registered, so once again, that annoying error when I'm trying to open any of my books (both mobi and azw3), is there:
"An error occurred. If you purchased this item from Amazon, delete the item and download it from the Cloud."
2nd try to recover:
- I've disabled
Whispersync for Books
Menu -> Settings -> Device Options -> Advanced Options
The result: I can open AZW3 files, but still can't open mobi...
One step at a time... I'll keep you posted.
At least for the reason that I've understood that I'm through the less, having 5.8.11 with all the goodies from here.
Misc
From time to time, KUAL give 2 errors at start:

(nothing new, it's in the
FAQ)
and after that, one more:
Giving CLOSE and CANCEL, I saved my KV from restarting and got KUAL to start. After the 2nd error KUAL starts.
Once started, I can start it again later, without any problem, but... in a while, the error(s) show up again.
I've used
Purge menu cache, but no help. Sooner or later, the error is UP.
It's a known behave, as I've seen.
I'll try to install GNU Awk.
...and I'll be back
All the best!