I love the HDR filter, that looks very realistic!
I like it very much myself, and have tested it quite a bit and think it is safe.
I've updated the d3dx.txt file in the OP to include this and a couple other changes. Just redownload the file and replace the original. As with everything, the effect can be turned off by commenting the code.
Here's a picture of Mercury:
The dark side is black as black can be, which looks extra good with a black sky. Unfortunately non-landable planets still have "bright" dark sides, for whatever reason. Still, the "HDR" look makes everything feel much more like "in space" realistic IMO, so give it a try!
As for the details of "how", let me get back to you on that. It's a bit complicated and I'm still figuring a few things out (I just started playing with it today, LOL).