If you want to lead some sort of rogue expedition, just find yourself a lord who supports your idea, have him create an army and find volunteers. You could even skip the army part though I wouldn't advise that unless you really want to go under the radar but that's pretty much impossible. Someone will always notice. Or how were you planning on hiding the battlereports from your realm?
If someone takes interest in what you are doing, that is exactly what needs to happen. If your realm is indeed eternally at peace, why not bring your plan to the realm for discussion and if they don't give you their support, attack their lack of bloodlust. Ask why they still call themselves warriors, or whatever. The fact that someone notices that you're doing something that you "shouldn't" be doing and takes an interest in it can only enhance the roleplay around your plans, not diminish it.
