What effect does the knowledge of a demon's true name have on the summoning process besides the fact that you can call the exact being?
no saving throw allowed in the binding :D
And no doubt a huge bonus in the deal making.. after all you have that demon at your beck and call..
At least until they have their true name changed..
Speaking of which, what is that lesser demon lord of poison supposed to look like.. suppose something could be worked out from shamis stats. And hopefully some poison that affects demons too ;)
I remember reading in the Book of Exalted Deeds something about poison like materials that could be applied to weapons to hurt evil outsiders real good.
Can you change truenames?
As I recall, Tome of Magic has a Ritual of Renaming which allows a being to change their truename. It isn't cheap, it isn't easy, and it's not fun, but anyone who gets tired of being summoned with their truename will probably look into it sooner or later...