Well you can change or add photos or clip art pretty easily though I don't know where you would place it for Design Pro to see it all the time as I have usually used it in a 'one design' use myself.
If you pull up the template design you want to use, just click the "Image" button on the top of the screen (as shown in the example below). Then click the "Browse" button at the bottom left and find your clip art. When you click "OK" when you have found it, it will be inserted in the document.
You can then resize it, move it, etc.-- and if you want to get rid of a graphic in the original template, just click it to select it use 'Edit-->Delete' to get rid of it.
Hope this helps- example below.