You can't just rename the file, to rename KUAL you would have to recompilie it with different name from its source code.
Since I've just now noticed that Amazon removed "Active" filter option (which was somewhat quicker way to display just KUAL as the only active content type "book") from "All Items, Books, Docs,Collection" dropdown menu (when did that happen??) the only thing left that you can do is manual search for KUAL then open it.
Or you could start using
KPVBooklet to be able to open PDFs and EPUBs in KOreader by click in book cover displayed on Kindle's Cover View, instead of opening KOreader via KUAL and then fopening the book you want to read.