I actually made these ages ago but completely forgot to upload it lol.
Anyway this is a simple replacement/override of the reins to make them thicker and less string-like. I also edited the uv to pick up a tiny portion of the texture from the bridle (specifically the top of the crownpiece) so that they'll automatically match the color of whatever bridle (or other headgear) the horse is wearing.
A few notes:
Because it's taking a few pixels of the bridle texture and stretching it out over the entire reins the rein texture might, as a side effect, look a bit flat and occasionally smudgy (depending on the bridle). I did try at first to sample a bigger bart of the bridle texture but that would create bigger visual issues with some bridles (especially cc ones), so this was the best compromise.
On another note, the reins are adjusted to match up with the maxis bridles and thus might not "attach" properly to some custom bridles that have bit rings or shanks that are lower down on the horse's face. This I also can't really do much about unfortunately.
Another side effect is that if you use a no-bridle mod the reins will appear solid black.