One function - Multiple MovieClips?

This is a question that has been haunting me for years-

Is there a way to apply one function to several MC's?
And how complicated is it?

It depends. Can you clarify what you are trying to achieve?

I have multiple MC's- all the same but duplicated.
I want to tell each one to preform an action once I click on it.
But I don't want to make an individual EventListener and a function for each one.

You can create a class, to which you associate the mc and add the functionality.