If it were easy, then it would probably work the same way as the male and female chars. Try typing the pk and mn char in the script, using copy-paste or whatever from the internet. If that works, have a look in PokemonSummary to see how the male and female chars are introduced. Then, have a look at some place where the trainer title (like Lass or Cooltrainer) is called (maybe in the compiler, but preferably closer to where the actual battle is called, have a look around), and do something like if it says pkmn then change it to charpk charmn. Know what I mean?
You'll probably fail to type the character in the script, however. Then I would advice to have a look at how the US dollar sign is replaced by the pokedollar sign. I don't know where to look then, but at least it's a start.
In general, I would say that implementing something that was originally implemented because they couldn't do better (apperently they couldn't fit in as many characters, and were forced to use an abbreviation) is a waste of your time. But I won't stop you :P
