You seem to be assuming that the eyeshadow is an opaque object, whose alpha value is adjusted at runtime within a limited range (e.g. 0% ... 60%). Therefore, we would simply need to
raise the upper limit in order to obtain very dark eyeshadow.
Actually, the eyeshadow sprite itself is
inherently semi-transparent; its gradient fill includes an alpha parameter. The game currently allows you to reach 100% opacity. The problem is that 100% opacity is not as dark as you would like it to be. It's
not possible to exceed 100% opacity by applying a transformation at runtime.
Therefore, you would need to extract the eyeshadow sprites from
SDT.swf (via
ffdec - check the range 1183 to 1223), manipulate them in a vector artwork program such as
Inkscape (and/or draw new sprites which fits the same shape), write some ActionScript to replace the original eyeshadow sprites with your new versions, and then publish the whole thing as a SWF file.
Of course, you don't need to do it all in the order I've listed. It would be a good idea to focus on one element (e.g. the lower-eyelid makeup) first, and then work on the others after you've proven that the technique will be effective.
If you don't know how to use Flash (and you aren't willing to learn) then you could simply share SVG files for the new/revised eyeshadow sprites. You could then ask the forum's Flash modders to package your artwork into a SWF mod and write the necessary code.