Incase you want to add a social web site that is not present in the current list in the admin panel. All you have to do is create an image icon of that site or download from internet (.png or .jpg or .gif), give it an appropriate name (e.g. Facebook.jpg or Facebook.png ) and drop it into the " social-web-links/images " folder in the plugin directory. NO NEED TO HACK THE CODE :). If you want to use your own set of icons, you can replace all the images in the " social-web-links/images " folder with your set of images.
Note there are two set of subfolder in images folder i.e. 16x16 and 26x26. They represent the size of icons. So when you add your own icon, make sure that your icon is of both sizes 16x16 and 26x26.