I believe you can have more than one anim, but, I am not sure whether you need something extra to get them to be chosen randomly or whether the game chooses one itself automatically.
Anyway, I think if you make another intro you can put it in the same yourisland_anims folder along with the first one, just rename it to intro2.yourisland.
You will need to list the cutscenes in your island config.cpp though, like so:
cutscenes[] = {"..\addons\yourisland_anims\intro","..\addons\yourisland_anims\intro2"};
Planck