Well, one of the good things of having a buggy experience changing things is that you learn new things as you go. I'm posting this here in case someone else needs the help switching boot animations back and forth, and can only boot correctly to recovery after installing something that didn't work right, and forgetting to back up first, like I did.
I thought I would have to do something complicated to get my phone working correctly again, but If you installed an animation that hangs your phone and are having boot issues:
A custom recovery that includes some basic file management functions, (like TWRP,) can help.
I found out you can install a bootanimation.zip file that is known to work on /data/local, and your phone will play that at boot.
This is a far easier path to getting your phone booting normally again than trying to get at the bootanimation.zip on /system/media from recovery. After your phone has booted again, you can use your favorite file manager (like Root Explorer,) to fix things back the way you wanted them if you do not want to leave a bootanimation.zip file in the /data/local folder, and want to muck back around system/media.
Is /data/local writable by default when mounted ? (ie can you adb push a file there in a hurry during the boot sequence before it hangs ?) If so, then it's by far the easiest solution and would not require a reflash should anyone be stuck and with locked bootloader (ie no custom recovery).
If adb push is too slow to send he file before hanging, another solution would be to use a computer to store a correct bootanimation.zip on the sdcard, then use adb shell mv /mount/sdcard1/bootanimation.zip /data/local
