People have been making mods for The Witcher 3 since the game came out, like ones that increase your weight limit or give the vendors more money, or the one that revealed that when Geralt's not around the NPCs devolve into melt-faced monstrosities. But CD Projekt Red wanted to support modders properly, so as of today there's an official Modkit.
CD Projekt Red chose to advertise the Modkit with a bit of unicorn facepaint. Want to show that you've got a better imagination? Head over to nexusmods.com to download the Modkit and grab the sample mods. The documentation explains how to use the tools to change meshes and textures for things like Geralt's clothing—shirts, trousers, boots—and his trusty steed. You can also edit scripts, but it's too early to tell how much of the game modders will really be able to mess with.
What mods would you like to see the community create first?