When I had os4; I copied the theme folder from /lib/plymouth/themes/zorin-od-plymouth to a backup drive then modified the images to suit my needs in the gimp. Once I had OS5 Installed, I copied my backup folder to the same directory overwriting the contents there. Then I downloaded and installed "Zorin Splashscreen Manager" HERE
. Upon running the manager I selected the folder I copied my modified contents to and VIOLA! I have my own customised splash screen with TUX! You can use this same method to get your sunrise animation back. I hope this is useful to you.
Note... I am a newbie when it comes to Linux... Not really much for playing with code, but I love to tinker with graphics. It stands to reason that you can copy the default sunrise directory without modification to /lib/plymouth/themes/ and it should work when selected in the Splashscreen manager.
I hope this is useful to you.