Wow, that was fast! I've tested it, and it indeed results in my vassal being automatically released when I win the siege - I wasn't even sure it worked at first, since there's no message. Thanks a lot, this is one of those glaring omissions in the base game.
I noticed it also adds a (random?) event when you win a siege. It's buggy though, it told me that the Sheikh was among those present and asked me whether I wanted to take prisoners, kill everyone or leave them be. I chose the option to capture everyone of importance, but he wasn't captured. It might make sense since his status said he was busy doing a council mission somewhere else - I guess the event doesn't take that into account. Might be nice to fix that bug but I don't care much for this event in its current form - the mandatory trait changes are rather annoying and are IMO ahistorical: taking prisoners after a siege wouldn't be considered as uncharitable, actually AFAIK killing everyone inside was pretty much the default option. And perhaps I want to not take any prisoners to save myself the management hassle, without losing the Cruel trait which has its uses.
Pared down to just the prisoner release feature, this would be worthy of being released on the Steam Workshop. My mind was blow when I realized that nothing of the sort existed.
(To make it perfect I think it'd just need a message to tell you you freed someone, and some positive modifier on the person whose ass you dragged out of prison.)
