Go locker fourkey theme - how to change icons?

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http://forums.androidcentral.com – I am using Go Launcher Ex and Go Locker. My lock screen theme is Fourkey. The four default choices are home screen, SMS, Phone, and Camera. I read somewhere that you can customize these icons? Is that possible? If so, how do I do that? I want to replace the Camera icon with my AquaMail icon. Thanks. (HowTos)