I'm going to have to dig out some of my stuff, but I wasn't envisaging anything quite so complicated. Why do you want to feed the skin texture into the Bump input? Yes, there is a way to do invert the basic map. Use a math node, and multiply by -1. Then the black parts of the map are translated to white, and vice versa. Use a smaller absolute value to reduce the range of the result, and another math node can shift the value. All the math nodes are listed in Chapter 43 of the manual. I'm now trying to find out if black=0 or black=1, it doesn't seem to get mentioned. I think if you want to figure out what is happening, that last screen-grab i9s getting too complicated.