At some point in the game, neutral "Faction Buildings" can be renovated for one of the three factions: Courtesans, Thieves, or Mercenaries. Other than getting quick access to that particular faction, is there any advantage or disadvantage inherent in this choice? Also, can I change my mind later?
Renovating faction buildings aren't too rewarding IMHO. Sure they give you income and make faction members available in the district, but in my personal experience, I never needed a faction's help except in the forced missions. There's no real disadvantage to it other than a loss of some coin (but that's a given) and you can only have a single faction in the district at a time. But then again, I don't feel you really need their help.
You can however always change factions after renovating for another. You'll just have to pay for the renovation again for the next faction.