Note; Code based on an example here
For a long time I figured that there was little you can do to edit such fine aspects of a material in the BGE such as specularity, simply because the functions that did those did not work in GLSL, it almost seemed like you would need to go to another engine to have games with neat looking material changes.
However, people who figured that it was the case is wrong (thanks to what is possibly a little known fact about the possibilities of video texture).
In the .blend, once unzipped, use the left and right arrow keys and watch the specularity get rougher, the specularity get dimmer, and the color more blue in realtime and in GLSL (with no vertex color tricks, replace mesh tricks, or any other hacks or workarounds). I have found that any material property that can be manipulated by a normal texture can be manipulated by a video texture as well.