Coincidence? Or a broken fan?
Just after playing with the boot screen and login screen modifications, the laptop seems to be over-heating. At least, the video is going all flickery which in a laptop is usually a good sign that heat is not being handled correctly. While warm to the touch on the bottom, the heat does not feel excessive, and the fan isn't running. (Maybe the fan is broken?)
I've backed out the changes on the laptop for now, but that hasn't had an effect on the system yet. I think it might be the fan.