You need to edit the file /User/Library/Preferences/com.apple.Preferences.plist on the device -> whether you use a jailbreak to achieve this or merely some iTunes backup editor is up to you.
Add the following boolean key as ‘true’:
Enabling Emoji Icon Using Cydia
For jailbreak iPhone user with Cydia installed, you do not need to edit this value manually. Cydia does all the stuffs for you. What you have to do is to open up Cydia and install Emoji under Tweaks section.
After installation, go to “Settings” -> “General” -> “International” -> “Keyboards” -> “Japanese”. Then switch on Emoji to enable Emoji icons.
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