The official faction has almost never had problems with unofficial IMG factions. In fact, cooperation sometimes was rather close and created nice rp.
So, of course you can use the IMG ID for your shadier approach. It's in the nature of a Guild to give freedom to the individual.
Just one thing that I want to clarify: The official faction does not take any responsibility for your shady/unlawful actions, just because you fly the ID.
If you, as an extreme example, piss off a whole house, the official faction will not take the responsibility for your actions, nor automatically defend you against their wrath. =)
I clarify that right here, because we had an IMG faction before (today's Rotfront) who changed ID in the end (to Hessian) because the rift between their unlawful rp and the "mainstream" lawful approach of the official faction became too wide. It was a little messy and I would like to avoid a repetition of it.
I hope you have fun and I bet we will meet. I am hoping for nice interaction and interesting roleplay. Good luck!