When I was first working on Unicode Font Hack for Kindle 2 I bricked mine by messing up the fonts configuration. This prevented Java GUI from starting up so I had to way to install an update that would reverse the change.
While this hack will not fix your already bricked Kindle it will give you a chance to unbrick yours in the future. All it does is it installs a startup script that would scan check system directory for exec.sh and execute commands that are in there. File is then renamed to exec.sh.done to avoid infinite executions. This will give you a chance to run some commands even if Java GUI doesn’t start for one reason or another. It will also give you ability to run commands on your Kindle without having to roll updates for every command, use serial console or USB networking hack.
Since this gives you the ability to run any commands on your Kindle this surely gives you the ability to irreversibly brick it as well. So if you don’t know your way around Linux I don’t recommend you install it at all.
That being said, the hack can be downloaded here: kindle_antibrick.zip
All you need to do is copy appropriate (update_antibrick-k2.bin for Kindle 2, update_antibrick-kdx for Kindle DX and update_antibrick-k2i for Kindle International) file into root directory of Kindle USB drive just like any other hack. It will also copy small sample exec.sh into system directory. Upon successful installation this script will create a file antibrick-success.txt in the root folder.
Since it doesn’t change any existing files it is not intrusive in regard to official Amazon updates and will not prevent them from being installed.
update_antibrick_remove-*.bin files remove the hack. Once again you should use the file that corresponds to your device version.
I’ve decided to publish this before I publish the updated Unicode Fonts hack so that people who would want to modify the hack may install this first.