I followed what you had said, d/l from the app store and moving it. When I was in settings it had a message in red about going to recently used apps and removing other loaders listed. I will check when I get home and see if it is still there.
Ok. I will rephrase what I said. Delete "com.anddoes.xxxx(I forgot but it starts with that) from data/app, if its there. Then delete from system/app (it should be there, either as Apex Launcher or com.anddoes) .Then reboot, and install apex from play store. Then find it in DATA/APP and MOVE IT to SYSTEM/APP. Change properties to User: Read Write Group: RW Other: RW. Then you can reboot your Kindle. Then it should say "Kindle is upgrading, and then choose which launcher you want.