Descr Character.txt lists different types of Characters/Agents and what they can do(If it walks outside a city or is on the sea then it's abilities a.k.a. actions are listed here). Through this you can remove certain "right click" abilities as well as other abilities on the strategy map. For instance you could remove bribing from the game by removing bribe from the diplomat characters actions. Or you can make something immobile by removing the move action.
Giving a character too many right click commands could potentially cause problems but Princesses can go in diplomacy or marry... two quite different things.
List of commands in M2TW: moving_normal, moving_quickmarch, garrison, assault, attack, besiege, entrench, ambush, diplomacy, bribe, exchange, building_fort, building_watchtower, Spying, assassinate, sabotage, diplomacy, bribe, quick_sail, blockade, disembark, marry, acquire, denounce.
Although interestingly... there is no Recruit_Mercanary action so this means that you probably cannot ever give captains the ability to recruit mercenaries. However you can allow them to do most of the things above (probably can't disembark).
Notable things that probably need to be Further Elaborated: Garrison: I suspect this is just garrisoning a settlement or fort Entranch: ? (Give to generals) Exchange: ? (Given to generals) Aquire: This is the merchant acquire goods ability... although in effect it basically kills the enemy merchant after a stat based roll Spying(Given to spies): What exactly does this do? Does it make a character invisible? Does it allow a character to see invisible units? Does it allow a character to open gates? Quick sail: What does this do? How do you do it? Moving Quickmarch: I suspect similar to above