Hi,
I am not aware of any find and replace methods.
If you have/make Object_A as a prefab. What you can do is drag Object_B over the prefab in the project window while holding the ALT key and it will give you the option to replace Object_A with Object_B. This should then keep your references to all your actions.
The only other way I can think of, which I use all the time, is to have a variable that all the actions use. So you are not dragging Object_A into each action everytime but rather selecting the variable. Global variables are good for this as they can be used between FSM's. With this variable setup, you can then update and change the references back and forth between Object_A and Object_B as you want.