I don't quite understand what you're trying to do... If you need something changed like that, why not have your button notify a manager script, and have the manager do the rest? Why do you need to change the target? Central manager script is the key.
Cause in this way i have to manage all the uibuttons and sliders in this manager (there are several buttons with two different uibuttonsendmessage scripts, one used to close the window and the other to send the message to the manager plus the uislider script). So in this way i have to assign the central manager all uibuttonsendmessage and uislider script to the manager, and every time the UI changes, i have to change the central manager code accordingly.
While, if i change directly the target game object object, i dont have to change anything in the code, just the UI in the inspector.
Hope now its more clear.