Comment by TazeTSchnitzel

I think I remember using one of these apps around 2010 or so, and I think it just triggered the emoji keyboard to appear somehow? And once it was opened once, the ability to use it persisted. But that was just my guess as to what was happening as a user.

I really doubt Apple's sandbox would have permitted editing a global preferences file like that. That might have just been the first, and not the only, method to enable emoji that people discovered.