The prop is effectively using a skin transplant to cover the existing brows. You have the same skin applied to the eyebrow as is applied to Genesis, but the eyebrow prop is set up to use a different part of the map so that it won’t have eyebrows. on it. The opacity map fades the graft layer around the edges, with the result that it blends in to the texture on Genesis (as long as there are aren’t any patterns on the skin, such as tattoos or scars). That gives you a browless Genesis, then you apply the eyebrow you want to the prop to finish the process. If you are using a skin texture that is already browless you don’t need the skin-transplant to cover the brows, and for that you can simply remove the transparency map from the eyebrow prop’s SkinFace material and set the opacity to 0.
The first image shows Genesis with the Aiden for m5 textures
Then I add the eyebrow
With the brow selected I apply the Aiden material to it with the preset
Then I go to the Eyebrow materials folder and apply the one I want
That softens the edge of the eyebrow, and loads the brow image, the preview isn’t clear but the render shows the end result - in this case you can see the edge of the brow plate, that will vary by character set depending on how much tonal variation there is across the head but it can be softened in post work if need be.