This would be easy to do in photoshop if you have it, gimp 2.8 is also a great software to use for this.
It's just like making a preset, really, just with different names~
Make sure that it is a 512x512 canvas on grayscale, not RGB colour. The background needs to be white and you could use fur brushes to mark out the texture using different shades of gray, using a UV reference from your "My_Presets" folder. Open that up on another layer and once you're done with your fur texture, delete/hide the UV reference layer and save the canvas as "cbodyShade, ctailShade, cheadShade..." etc. Use "f" instead of "c" if its a feline texture. Remember to save this as a .jpeg file into your "FeralHeart\Media\Textures".
Feel free to PM me if you need any more assistance with this~