What do you mean by opening screen?
1) The splash-screens that show up before you even get to the menu?
2) Or the little cutscene playing behind the menu?
Well, the answers are:
1) Probably not, as these are most likely coded into the game.
2) Yeppers. These are just cutscenes made on the different islands. And if you make your own island addon with a cutscene, and write up a new config.cpp to have it start with that island in the background, you can do it.