The issue with blackmail in nearly every instance in Disco is that when it involves quasilawful factions there's a very good chance that it'll backfire, especially if attempting to blackmail / extort a member that isnt actually part of any tagged faction.
All conversation logs are recorded, so attempting to actually blackmail another person can very easily end in the attempted blackmailer getting in more trouble than the actual person being blackmailed, who as an individual DOES unfortunately have access to /rename commands while as a tagged faction your entire group can be held liable with no chance to escape consequences. Even then, telling someone you're going to report them can have other consequences for the reporter if they give any kind of indication inrp of their intentions.
This isnt really an ideal situation but to the best of my own knowledge there really isnt any other way for it to be handled that's actually safe for the one with the evidence, though I do understand the frustration and concern.