Let's say I have a graphic on the time line, and I want to change it (without cutting it out and replacing) is there a way to click on it and replace it with another graphic?
Right click and choose "Select in Media Pool" then go to your media pool, find it, right click and choose "Replace." Find the emdia you want and it will be replaced (keep in mind, it will be replaced EVERYWHERE else it appeared in the project).
In the media pool right click the graphic you wish to use and drag it on top of the graphic in the timeline. Then choose Add as Take from the popup menu.
To switch between multiple takes, select the graphic and press T.