"La kvin talentaj aktoroj rolis kiel gardistoj en la teatro."
Translation:The five talented actors performed as guards in the theater.
To say that "the five talented actors acted AS guards in the theater" is different from saying that "the five talented actors acted LIKE guards in the theater." In the first sentence, the actors could be doing side work as guards, while in the second sentence the actors are merely acting like guards, while not actually being guards.
Yes, you are right. Kiel can have a meaning of similarity, identity or role. There have been proposals to use other words to distinguish these three, but it was not successful because you normally you can tell from the context.