No offence but you really need to read at least the first comment of Downgrader 2.0 thread and in general understand what exactly you are doing and why you're doing that.
Like why you need to change that "version" file and why each Kindle model has its own build value.
And that there are 3 different ways of changing that were mentioned thus far:
1) The "normal" one : running Downgrader 2.0 KUAL extension. Not a possibility for you since you don't have working KUAL.
2) using " ;log runme" to run any arbitrary shell code. @Marek used that to modify the version file in order do be able to downgrade firmware.
I'm not clear (since you didn't write clearly and in details) what things you did or didn't try, thus don't know if " ;log mrpi" and/or " ;log runme" search bar commands are working on your device at this moment in time.
So try both and let us know.
3) emergency thing is meant to try and restore "jailbreak bridge" system of scripts and commands, when some are broken by a firmware update.
As a bonus you're instructed to edit that script file in order to make it also do that version file edits in order to enable you to later do a firmware downgrade.
If you can't use " ;log runme" then this is the last remaining possibility to run a shell script.
If emergency things is successful in restoring jailbreak bridge things after it is run you should have both ";log mrpi" and " ;log runme" functioning again.
Do you have version.txt.backup file visible on your Kindle drive when you connect Kindle to your computer?
In order to use KUAL and KOReader you must have a firmware that is not 5.16.3 or newer (so the cutoff firmware version is 5.16.2.1.1). That is why you need do downgrade back to 5.16.2.1.1 (and to downgrade you need functioning jailbreak and ability to run scripts and shell code, because you need that to modify that version.txt file).
So, after doing the emergency stuff do 2 mode reboot. Then test if ";log mrpi" command works or not.
Then download the official firmware binary for your PW4 from Amazon servers, no need for SoftPedia, here is the link:
Code:
https://s3.amazonaws.com/firmwaredownloads/update_kindle_all_new_paperwhite_v2_5.16.2.1.1.bin
By doing the rest of downgrade procedure (you already took care of modifying the version.txt, now copy the bin to Kindle drive and do the rest as instructed), IIRC you need to force a device reboot without ejecting and unplugging the USB cable from your computer?
If you manage to downgrade to firmware 5.16.2.1.1 do couple more reboots and then try to install the hotfix bin using "Update Your Kindle" option.