I guess you’d have to be careful with the way you add the charred marks. On the other hand, the real siding wouldn’t be seamless. You could take a seamless texture and copy it enough times to make siding that is a bit longer than you’d need. Add the charring to that long texture.
All the wood grain textures I make are 6 feet to 14 feet long depending on the species. Of course I’m using images of real boards but you could fake it in Photoshop. You could make several versions so that you can avoid too much repetition.