I have not had a chance yet to work on the file you sent me to look at.
It seems like the normal maps are not correct based on what I did see but I myself don't use a plugin for 3ds max to edit things like this....I just export the model .obj and just edit it that way and make a brand new texture after I do my edits. My method is somewhat different then what others here likely do.
But then, I never was able to get any .nif plugin for 3ds max to ever work on my end regardless what version of 3ds I bother using (have every version...rofl) or settings that are used. So in effect I basicly created my own technique while...a little harder...works quite well for me.
SWEGTA here has used the plugin and likely has had better luck then most people that have used it. MadHattrick also uses the plugin if memory serves here...and also can do quite a lot with all of this.