Well, it'd be pretty neat to be able to disguise oneself and do things like that, but really that's only if the AI can handle it. If something like that's implemented and the AI isn't cabable of doing anything if they find out you're the one behind the attacks (and as such, there's nothing to deter you from doing it), then it'd be a very broken mechanic. EVERY player would do this, as there'd be no drawbacks and tremendous rewards (you get free loot and the village loves you), so it'd be stupid not to. Heck, players would probably do this in every town they come across. Unless you're considering the actual battle where the player may get killed. But I digress. However, having something like this to be part of a feature list (as in: here's a list of cool specific things you can do that we've added) seems kind of werid.
Really the best way (in my opinion, anyways) for things involving NPCs and getting them to attack towns and such or doing whatever really would be to maybe not make it a preset feature, but have complex enough NPCs instead, to make things like this possible. So, you pick a target village, talk with NPCs there, make sure you're known there, and make up some story about travelling to some far-off location. Then, get some thugs together who want to wreck and steal stuff and are willing to be in your team, and go attack the village (by ordering them to attack a specific area, see? so you could use it anywhere, really), wearing a mask or something to obsure your face and making sure not to wear similar clothes or talk to anyone (they might recognise your voice, maybe?). Doing that would make any NPC not recognise you in any situation, not just that specific one.
Once you've looted the place and scared some of the villagers, they'll start rebuilding the village, and, a few days later, you show up and help out and donate money (not donating any treasures you stole, just generic money, as NPCs may recognise the treasure), and the villager's view of you improves.
Basically, what I'm trying to say is that it'd be better to implement complex AI that have the behaviours and thoughts that could allow you to pull off things like this and other dastardly deeds.
Because who doesn't love dastardly deeds?