You can change the icon and pick anything you like but I am unsure if you can make only one icon bigger.
You could maybe create a picture with instructions to click the icon that leads to the card and use the picture as your background if no one comes up with a way of doing it. Its fairly simple to do that just pick a picture add some text save it and right click on it and select "set as desktop background". picture can be anything you like
Just a thought.