It's not too bad of an idea. Whilst the idea of a "rogue" class of nobility is silly (you've got trader or infiltrator, or messaging/deals/alliances) to play that out, adventurers can also fulfill the role to a certain degree. Low chances of success, little but useful information gained, no major realm changing events. Can join guilds just as easily as nobles (for 5 gold, then set borrowing limits relatively high). As spies they're excellent, very low cost, and can be quite interesting to play. But this is a digression, it's up to you to flesh out a roguish character of whatever class, there are enough mechanics and RP opportunities to do so.
But a mercenary class? Is it possible under the current game mechanics? You could just ask for bonds and stipends from nobles in your realm, but it does mean that you need a good idea of alliances and bank locations to change them out on the field. As a group of mercenaries from one realm it also brings up the question of three sided battles or the ability to attack your realm's ally's lands.
I find it an interesting subject simply for the mechanics of whether it can be done successfully and for how long. As well as the inevitable consequences of it in realm diplomacy. Various examples exist in history, some well outside the time period or scope of BM, but it may be an interesting character concept. For some reason the privateers of the Carribean come to mind of the consequences of these action. Both sides may end up declaring you pirate and decide to hang you.
Never-the-less....... Sick of LN's drivel with an established character? Get orders, get money, get friends, go fight a private war. Make sure they're good friends or you'll get banned from your realm. Make sure they pay you a lot. What will happen during a three-sided battle, or when you and your company of mercs all being set to murderous so you can attack supposed allies is up to the dice gods.
Sounds horribly fun really.
