Actually you can use an app called Awesome Icons from the Play Store. Once installed, add an Awesome Icon Shortcut Widget, and choose the app you want to have a custom icon for. Then select 'icon pack' when choosing your icon and select your Viral Icon Pack.
Some note on usage:
1. You need to set each icon shortcut individually.
2. If you have to restart your phone at any point , the shortcuts will temporarily change back to the default app icon. When this happens, just open settings > Wallpaper & Style and toggle the 'Themed Icons' button on then off.
