Ah, well as Daryk mentioned Pirate hunting is a notable possibility.
Of course, coming back to the neo-feudalistic nature of the Inner Sphere warfare between petty nobles is basically inseparable from piracy. I say pirate hunting, you say *I'm* the pirates. He said she said. Still, if a force is small enough or being specific enough about what they're targeting, a raiding force taking on Count Dookienose's forces and not posing a threat to the rest of the planet might not even rise to the attention of the native House Army garrison. "Grow up and settle your squabbles with House Stuffybritches on your own, we've got better things to do than bail your sorry ass out."
The MRBC can provide a completely different angle. If your contract is certified, you presumably have some kind of IFF code you can use to broadcast your legitimate status. If you're not being paid to take over the world, presumably you'll be happy to admit to that and prove it through ComStar if the native House garrison takes an interest in your presence.