[Wear OS Software and Hacking General] [NUMINIT]:
Yes, it's possible, and yes, it's pretty much exactly the same process as on your phone. If you've done it there, you can do it on Wear.

Oh, apologies if this is old news to you, but I couldn't find threads on this particular topic, and I'm quite satisfied that it worked, so why not share.

Now, the stock Wear boot animation is great. I personally love it, at least -- so why change it? Well, why do we do most things on XDA? Because we can. Do at your own risk, I take no responsibility if you screw up. Take these notes as suggestions. I mean, they work, but you know. Backups are always a good idea.

tl;dr for people who don't need help with adb:

push the bootanimation.zip to /system/media (back up the original!), then

chmod 644 bootanimation.zip

reboot

done.

Stuff you'll need:

1. An Android Wear device (any should do, I have a Sony Smartwatch 3) that has root access and ADB debugging enabled

2. A custom kernel that has adbd insecure (I used this)

3. ADB drivers on your computer

4. A boot animation. Duh. I used this for testing purposes because the resolution is meh x close enough.

Optional: a file explorer that works on Wear. I use ES.

How to do it (the way I did, I know there are other ways):

1. On your computer: move the .zip file your animation comes in to the folder where you have ADB installed. It's probably something like "C:\Users\yourname\AppData\Local\Android\android-sdk\platform-tools".

2. Open a command window in that location by shift+right clicking on the folder and selecting "Open command window here".

3. Connect your watch to your computer no later than now. If prompted, allow debugging (note that if it's your first time, the prompt should show. If not, check developer settings again).

4. In the command prompt, type

adb devices

This lists the devices that are connected to your computer. You should see the text "List of devices attached", your watch's serial number, and the text "device" next to it. If you don't, check your drivers.

5. Copy the .zip onto your watch:

adb push bootanimation.zip /sdcard/

The directory doesn't actually matter, just make sure it's not /system and somewhere you can remember.

6. Why not /system? Because it's, by default, a read-only partition we can't access via normal adb commands. Yet that's where that zip is headed. This is where the adbd insecure kernel comes in: with it, you can remount /system as read-write. For that, enter the adb shell:

adb shell

It'll show (don't write this!)

shell@tetra:/ $

To get the root privileges you'll need, type

su

What you should get is

shell@tetra:/ $ su
root@tetra:/ #

The # means you're rooted. If it shows without typing "su," great.

7. Remount /system as read-write by typing the following:

mount -o rw,remount /system

8. We can now alter the partition, and we'll start by backing up your stock boot animation. To do that, we need to "move" the file to an identical file with a different name. If that sounds like it doesn't make sense, that's because it doesn't -- it's stupid, but adb shell doesn't have a rename command. This is to avoid the stock animation from getting overwritten by the new one if anything goes wrong. Anyway, to accomplish that, type

mv /system/media/bootanimation.zip bootanimation.zip1

This changes the animation's extension to .zip1, which doesn't exist. The point of this is that Android looks for /system/media/bootanimation.zip when booting up, so "bootanimation.zip1" gets ignored and is out of our way. If you'd reboot the watch now, there would be no boot animation, just a plain "Android" text (or as is the case with my 320x320 SW3, "NDROI")

9. Now we'll need to move our new animation to replace the old one. To accomplish that, use the aforementioned "move" command:

mv /sdcard/bootanimation.zip /system/media/

10. Finally, to make the animation actually display, we'll need to give it proper permissions, which are rw-r-r. "chmod" is the command that alters permissions, rw is represented by a six, and r by a four.

chmod 644 /system/media/bootanimation.zip

11. Close down /system

mount -o ro,remount /system

12. Done! Reboot your watch and enjoy your new boot animation!