As "Extort Tribute" is essentially a renaming of the old Tributary CB, maybe there is another 7th one added in the DLC.
Yes, there's another one - Nomad Tributary.

It's a type of Tributary specifically tailored for use by Nomads. It's much more powerful than the other Tributary types, it takes 50% of their income and saps some prestige from them to you. It persists through death like a Tributary State, and unlike Tributary States the suzerain does not have to defend them if they don't want to.
One more potential one they could add is to seize all (or more than one of) the holdings of the target that are inside your realm. Currently you can only take one at a time, which is a bitch when there are like 5 and every one causes a ten year truce.
I like this idea... I'll note it down for the future.
I firstly will mod out Free Hostages... hostages were taken to prevent war not to force a war... If somebody declares war to you to free a hostage... you should be able to execute the hostage without malus.
Who's said that you can't execute them without a malus?

Using the CB is a gamble, for obvious reasons.