I want to know if it's possible to take an existing pattern and darken some or all of the colors? I want to know if the program will do it for me, so that I don't have to choose the colors?
I'm sorry but this is an issue that can only be handled manually. Floss colors do not always follow logical numbering systems and you may find yourself with the darkest in one group but another group would work that is darker.
That's possible. However, be aware that how the computer sees color is not the same as how you see color. With any conversion from image to pattern, there will be some "tweaking" of the pattern, including some color changes, to get the pattern you want.
I think I may have found a way to darken the colors before you upload an image. You do it in the upload image window under the adjustment tab. You can move the hue and saturation levels and it looks like it does a pretty good job. It takes a few minutes and you have to go back and forth in the preview window, but it's better than nothing.