While many think that Apple ships closed-source products that cannot be customized, there are still many ways you can customize your Apple products, such as by customizing the OS X El Capitan app icons. If, for any reason, you do not like the icon of an app and wish to change it to something else, you can do that by just using your Mac.
There are many apps with various icons, and you can bore easily of them after seeing them every day. By tinkering around with these icons and changing them to something of your liking, you can make your Mac truly yours.
Note: we also have a guide on how you can extract the icon of an app on your Mac.
Customizing the OS X El Capitan App Icons
1. First, you need to select an app whose icon you want to change. Most of your apps should be available in the Applications folder. Right-click on your chosen app and select “Get Info.”
2. Make sure an icon is available on your Mac that you want the default icon to be replaced with. You can search the Internet to find icon packs and can then apply them on your machine.
Right-click on the icon file and select “Open With” followed by “Preview” to open the icon in the Preview app on your Mac.
3. When the icon opens in Preview, click on the “Edit” menu and choose the option that says “Select All.” It will select the entire icon.
4. A dotted-line should appear around the icon that indicates the entire icon has been selected. Copy it by clicking on the “Edit” menu and selecting “Copy.”
5. Now that the new icon is copied to your clipboard, focus on the Get Info dialog box that you launched for your app. Click on the app icon, and then click the “Edit” menu followed by “Paste” to paste the new icon.
6. You may be asked to enter your username and password. If you are asked, enter and move forward.
7. You should now see the new icon taking place of the old one in the Get Info dialog box. It means you were successful.
8. While the Get Info dialog box shows your new icon, not all the places on your Mac will do so. In order for the changes to come into force, you need to restart your Mac. After doing so you will see the new icon at every place on your Mac.
If you would like to get the default icon back for any reason, you can do so by launching the Get Info dialog box for the app, selecting the icon and then pressing the “Delete” button on your keyboard. That should bring the default icon back to your app.
If you find that some of the apps on your Mac just do not have appropriate icons, you can changes those icons using the built-in OS features.