Anyway, I can certainly just make it up, but if there is a good set of rules on how it works, how accurate it is, and what sorts of uses it has in the Third Imperium, I'd like to use it. Does anyone know if such a thing exists?
Just to drag this discussion back on topic.
If you are seriously thinking about rules for manipulative psychohistory, I'd would strongly recommend the book Transhuman Space: Toxic Memes. Much of the description of how psychohistory works and how it makes changes to the larger populations maps pretty exactly onto how memetics works.
You will need to do some translation of the rules from both the GURPS to CT perspective and the Transhuman Space assumptions to the Traveller universe.