Modifying Textures

Can someone point me in the right direction on how to deal with tweaking a somewhat complicated texture? I have taken existing texture files before and edited them in my paint program. Sometimes it is very straightforward, and other times I have had to do some trial and error to get things to wrap properly.

Now I am trying to modify the "Long Island Mansion" house, so that it is 4 stories, instead of 3. I have simply created another instance of the second story and moved it up between the existing second and third stories.

I thought that it would be easy to fix the issues where the siding textures meet, but when I went to edit the texture file for the siding on one of the walls, it is not simply a picture of the rows of siding. What I need to do is to take the top row of the siding, which is currently black, and recolor it to match the rest of the siding on the panel. In the texture file, things are broken up into a much more complex way.

How would I go about editing this so that I can tell what parts of the wall I am dealing with? Do I need to send it to another tool?