If you ever wanted to change the quick access default application icons on Samsung Galaxy S2 you can do this by going to applications screen. For example as seen in the following image we have Phone, Contacts, Messaging and Applications as the default set of icons.
To change this first go to the applications page by touching Applications.
Then touch the menu button on the phone to activate the menu and select Edit. This will take you to edit screen view. Now it is simple as dragging the application icon you want on your quick access to the icon you need to be replaced.
When you are satisfied, touch on the back button to save the changes. If you need to ignore the changes press the middle button.
As seen in the following images I have replaced the Contacts with Play Movies. Also if you want you keep only 3 or less icons in quick access you can achieve this by deleting unwanted icons using the edit view.
Arjuna's space 