Do note that Wyll uses the basic HAIR_HUM_M_Dreads_Short_A.GR2 for hair, in-game called "Loomspun". This mod replaces that hair type, meaning that it will not be available to use for character creation, and anyone in the game that uses it will similarly have their hair replaced. There is no way around this that I know of. So don't use this mod if that's not a loss you can live with.
For current installation, extract to the \Data\ folder of BG3's installation directory. See "known issues" for details why this is necessary for now.
Finally, I know this mod works in the beginning of the game, but it is my understanding that certain events can affect the look and nature of your companions throughout the game. I cannot currently test this myself, and I am not sure what files will be used at such a time, so if there are any issues, I cannot promise that I can fix them until I can actually progress in the game - which there is no guarantee that I will be doing for many moons, as my partner-in-crime is intensely busy with life. However, any feedback is appreciated and I will take a look at things as time permits.
There are a number of known issues that I would love to fix, but that I need help finding how to fix, because the code and file structure is spaghetti. Just tracking down the right files for this took days, and even then some things flat-out does not seem to work (such as heterochromia), and most things are not named or foldered intuitively.
I claim no ownership or credit of any of this, and encourage anyone to pick it apart as they see fit or include it in whatever.
Have fun! ^^/