Hiya. I just found this thread and am also interested modifying the "Collection" Icon for my new paperwhite. It's horrible. Amazon's really letting me down with their lack of options for collections yet again...
To be sure I understand what's been found out so far:
Once my new Kindle is jailbroken I"ll be able to access it's files once in side the files i'll need to look for
LOCATION: embedded within /opt/amazon/ebook/lib/app_utilities.jar
ACCESS VIA: jar (a *nix utility similar to tar)"
So I'll have to play around with Java code to make changes. And the only thing I can change is the Collection image from what it is now to some other standard image, unless I want to go in a write a whole complicated bunch of code that will cause the program to seek out a different image depending on some collection specific data like the title perhaps. Then perhaps have a folder where collection cover images all go named after their collections to make life easy...
That really does sound like a lot of work. I'm fond enough of personalization to actually care enough to do this. I'm just not sure that my limited knowledge of Java is sufficient.