I can't promise you'll get to the right spot with this, but it may be worth a try. I wrote this
article on some of the locations of various things in WLM. There is a location for custom emoticons, but I'm guessing the default ones may be in there as well since this folder contained many entries even on a computer with a fresh and first time install of WLM - no custom emoticons at all on that machine.
However, all the files in these folders have gobbledegook names. You likely won't be able to figure out which are standard and which are custom, much less which emoticon you're looking at, but you're welcome to try. You may be able to open the files in a photo editor of some sort like Photoshop and figure out which is which.
I'd save the contents of the folder to a flash drive so you can just dump it back in if you find it all goes bad. Worst case scenario if all goes wrong is a repair of WLM to get the contents back. Just don't delete the folder itself. And as my article says - I can't be responsible if you choose to play with these folders - they are in the hidden files for a reason and there's always risk involved. But if you're like me - it's not so much risk as a challenge LOL!
Best of luck with this...if you find what you're looking for I'd love confimation (or not) if it was in the custom emotes folder like I'm guessing.