Some good food for thought here.

My two cents: PC SoB won't be some rank and file Sister just like every other character is a at least a lesser "noble" on his own. I mostly agree with Radwraith but aren't we making RT a bit to legal action-proof? I mean we're taking about **** inquisitors no some willy-nilly governors or IG generals. I understand influance system working in the Imperium yet still this is inquisitors's very own turf and by default they should've a neat edge here.

Consider: what should RT do to take down some random inquisitor by legal action only? If answer is the same or almost the same as in the case of inquisitor taking down RT then imho there's something wrong.

Unfortunately that's pretty much the way it would work. A RT could, if he felt it was warranted, petition to have the Inquisitor sanctioned for interfering with his Holy remit (The Warrant). This would probably trigger the same review process in reverse!

Remember: in the Byzantine structure of the Imperium there is only Bureaucracy! The Imperium functions very much like Colonial Europe. Slow communications mean that governmental actions are very slow to play out. Because of this the Status of a given Individual is key to how fast justice comes to them. For an average Imperial citizen it's pretty quick since an Arbites can pronounce sentence and carry it out on the spot! (They were borrowed from Judge Dredd after all.) For a RT or Inquisitor it's a lot tougher! These people are Peers of the Imperium! On the same order as Space Marine Chapter masters and Ecclesiarchs. They are notoriously difficult to take action against as the plaintiff must have the "standing" to bring such action. While actual Arbites Judges Have that standing so do RT's and Inquisitors. Even among their own ranks this is not an easy thing. When they start crossing it becomes even more difficult! The Soul Drinker's were a good example of exactly this kind of situation. An Astartes Chapter master is not someone you want to cross generally. Neither is an Inquisitor and Neither is a Rogue trader! The SoB is NOT a peer of the Imperium and for that matter, neither is her Canoness! They would have to petition a higher authority for actual legal action. Of course that does not stop them from taking direct action to destroy perceived Heresy. This could include purging the RT's Imperial assets in an attempt to bring him to them! Depending on the RT, This could set off a star spanning conflict that the Inquisition and the Adeptus Terra would only hear about after it was over! In this situation the winner writes the history books so the Authorities would more or less shrug!

The inquisition technically holds no sway over a RT, period. The Imperium is a feudal system, and they are of equal rank. To legally take action against the other, they have to go to someone of HIGHER rank, which in both parties cases is only the High Lords of Terra.

In addition, Rogue Traders are EXPECTED (and all but required to to their job, really) to be heretical to some degree. Especially in any dealings with Xenos. As the books state, many in the inquisition would love to declare most RTs heretics, but they simply aren't allowed to.

Except the Inquisition's entire purpose is to somewhat side-step the usual hierarchies. Yes Rogue Traders are peers of the Imperium, but so are planetary governours and those most certainly do fall under the perview of the inquisition.

However, that still doesn't mean that the inquisitor can judge a Rogue Trader as simply as he can judge other peers of the Imperium (and easy in this case of course still means literally buildings full of paper work, but that is why the adept is an archetypical Inquisitorial Acolyte). Because as you correctly said there are certain things that are expected of Rogue Traders. And the reason for that is that they literally have a piece of paper that says the can do those things.

And this leads to what we already know:

If you broker some xenos artefacts there is little an inquisitor can and will do.

If you open fire on the Scintillan system monitor ships, because they wouldn't surrender their vessels to you, they can and will.

When it comes to inquisitors vs rogue traders, its not so much an issue of necessarily revoking a warrant as it is an inquisitor going out of his or her way to really make things difficult for the dynasty. Yeah, Inquisitor X can't do anything about the Warrant or the fact that in the Expanse Rogue Trader A speaks with the voice of the Emperor. That said, the tithes and shipments headed back through Port Wander can be subject to searches and seizures which effectively cut off profits from reaching the dynasty at large, making trade difficult and cutting off resources for repairs and acquisitions out in the Expanse. If that goes on long enough, other RT's are likely to step in and take advantage.

Can RT's get around this? Of course, but a well connected Inquisitor is likely to be a major pain and bring about the downfall of a dynasty without touching the warrant directly.

I like that Regis a much more intelligent way to handle an Inquisitor taking exception with an RT and going about it in an intelligent manner.

It also adds a lot of role-playing and plot hooks for the campaign.

I guess the issue is this. An Inquisitor can't touch a RT Warrant or the family directly without concrete evidence, but ....... What happens when said Inquisitor makes it know to every associate, family member, rival, and employe that the Inquisition is looking into their organization. It's like saying I want to be affiliated with "enter well known franchise or important person" even though the FBI/KGB/Secret Service is looking at him/her/them for treason, criminal activity, weapons smuggling, human sex trafficking, bribery, murder, solicitation, conspiracy, blackmail, kidnapping, and jay walking. Not all of these will stick in a court of law (and maybe the Inquisitor isn't trying to make them stick, and is satisfied to spread rumors and randomly bang on your door at night, metaphorically speaking of course), but there goes your reputation.

Oh absolutely. I love that take on it and it's the most likely path an Inquisitor would take imo. Or sneaking a throne agent on ship or worse an assassin. The amount of clownpants nonsense a RT would have to get up to to justify a head on confrontation with the inquisition would be ridiculous. Though, if you look at that "you know you're playing RT when" thread....