Yep that's exactly the same problem. Changing position or orientation of any animated bones (which are all of them actually) has no effect during gameplay because the animation information overrides whatever changes you made.
What you could try and do is model the forearm and the hand in 3ds max, remove the default ones by making them tiny and put the new ones instead, which will allow you to orient them any way you want, but it's a complicated procedure (I tried) and requires a lot of work trying to properly position and orient them. Another problem with doing that is that the animation may look a bit strange since it was made with arm and hand being at certain angles, if you change those angles it might look weird and unnatural.
I think making changes like that using the NIF viewer only is a bit pushing it, at this point I think it's best to basically build a unit in max and animate there, which is not easy of course.
I'm hoping in a couple of weeks to get to that, as I'm going to model a human and try to export it using one of the sample files with animations. If that goes well then simple changes to those animations will follow to accomodate for various weapons, and then, well I don't want to get ahead of myself, but I've been scouring the net for good dragon illustrations... and btw, if anyone knows where I can get a good side/profile drawing of a dragon, with maybe a front view also, or better yet all 3 views (side, front, top) I'd be forever grateful.
and it also gives me the idea that perhaps if I make any head gear I could make hi-rez version of it so people can add it to the leaders. 
