Custom Name Tag Skins

I've been attempting to figure out how to give an entity a Custom Skin/Function when Name Tagged (Like when a Sheep is named jeb_, or a Vindicator is named Johnny).

As well as potentially Player Usernames (Like the developers Dinnerbone and Grumm being upside down, or Notch having once dropped apples on death.)

For context! I'm using MCreator version 2023.4 as well as the "Nerdy's GeckoLib Plugin" for that same version. (Big thanks to user "friyes" for helping me figure out my version was only for forge.)

I've been making steady progress with my first mod, having made an animated creature as well as started work on a few crop ideas. And I was wondering- would it be possible with MCreator to give an entity a custom skin and/or functionality when given a specific name with a name tag?

(as many gamers are prone to do, I want to make an easter egg)

But then I also began to wonder if it would be possible to have custom functionality for players with specific usernames? Because I think it would be a nice thing to do for my friends who have been helping me while also making mods of their own.

My biggest issue though, is that I'm just not quite certain how one would go about doing either of those two things.

If within MCreator, it simply isn't possible to give players their own unique trait, then I'll concede that. But since mobs getting special skins when named tagged is an inherently base-game function of Minecraft, I would hope at least that  would be something I could potentially accomplish.

And such is my question. How would I go about making the custom name tag easter-egg? Any help would be certainly, very much appreciated! I would love to be able to do both the player and mobs things, but would happily settle for just one! I'll of course continue to look into this myself, but I also send out this post in the hopes that someone more knowledgeable than I would be willing to provide their expertise!

-Thank you, and have a wonderful day!