Day one of having the Kindle Touch (KSO), and I started off the bat with a jailbreak and removing those pesky ads. After dumping my own copy of the rootfs of the Kindle Touch v5.0.0, I started to examine the directory layout. Within this, I found out how to 1) Disable ads for good (I don't know how to turn them back on [nor why anyone would want to] without a factory reset), 2) Change the Startup Splash/Reboot Splash/USB Connected splash/battery icons for USB screen, and 3) although I had kept reading it wouldn't work, alternating custom screensavers!
HERE BE DRAGONS!! If you mess up your device (somehow) in any way, I will not be held liable!
First two pictures are the Startup and Reboot splash.
Last 5 are the screensavers I'm now using.
Now, how did I make what is in those pictures come to be? Easy, File Replacement.
1) MAKE A BACKUP OF YOUR /usr/share/blanket/ DIRECTORY! This will also come in handy for file names.
2) For whatever image you would like to replace, overwrite the corresponding file on the kindle. For Example. If you want to replace the screensavers, and you only want 2 images, make sure you clear out the /usr/share/blanket/screensavers directory, then place your 2 screensavers in there, having the names bg_xsmall_ss00.png and bg_xsmall_ss01.png. You can see the pattern in that one. Make sure all images you're planning on replacing are 600x800 resolution and Greyscale.
PROTIP!: Everything I've found easy to replace has been in that blanket directory. I would recommend using ssh and sshfs, and transferring with Filezilla, since it makes this ALOT easier. Just make sure you ssh into your Kindle first and use the "mntroot rw" command if you've rebooted, to make your device writable.
After all of your files are finished being replaced, just simply reboot your device.