It is an option. It is possible, but not guaranteed. There are no guarantees in BattleMaster. You pay your money, you take your chances. It may take multiple attempts to make it work, but it can work. And you'd better be a good assassin. No newbie assassin who can't tell a shadow from a sunbeam, and doesn't know to take the dagger from the sheath before stabbing is going to hit a duke hard enough to knock him out. But if you get a world-class swordfighter who is also a ninja-class infiltrator, who buries that dagger deep into that octogenarian duke, he's going down for a LONG time. Probably. Again, no guarantees. But it is worth a shot.
I've tried. It is NOT an option. If not a single player can cite a single instance of this actually occurring in the past year let alone 3-5 years, then it isn't an option. The odds are either not high enough or some factor is off. A 1% chance is not a chance. If you seriously wound a Duke, they should lose their position 100% of the time. Serious wounds aren't easy to pull off, but if you do pull it off they should lose their position. (See new feature request as an addendum to this one)
Secede. Declare war. Conquer!
Damaging? Yes. Fun? Definitely!
I can't secede because my other feature request hasn't been approved yet to actually make secessions more reasonable. I can't declare war, because intra-realm warfare is banned. I can't conquer my own regions.
You're still missing the point though. The infiltrator class is pretty meaningless when their main action doesn't have any real in-game effect.
