BGE PyAPI support for subclassing any BGE game type from python, scripters define extra functions on gameObjects.

Adding a UI to set the type on startup can be added easily.

# ----
class myPlayer(GameTypes.KX_GameObject):
  def die(self):
    # ... do stuff ...
    self.endObject()

# make an instance
player = myPlayer(gameOb) # gameOb is made invalid now.
player.die()

# ----

One limitation (which could also be an advantage), is making the subclass instance will return that subclass everywhere, you cant have 2 different subclasses of the same BGE data at once.

source/blender/python/intern/bpy_rna.c

@@ -204,13 +204,13 @@ static long pyrna_struct_hash( BPy_StructRNA * self )
 /* use our own dealloc so we can free a property if we use one */
 static void pyrna_struct_dealloc( BPy_StructRNA * self )
 {
-	/* Note!! for some weired reason calling PyObject_DEL() directly crashes blender! */
 	if (self->freeptr && self->ptr.data) {
 		IDP_FreeProperty(self->ptr.data);
 		MEM_freeN(self->ptr.data);
 		self->ptr.data= NULL;
 	}
 
+	/* Note, for subclassed PyObjects we cant just call PyObject_DEL() directly or it will crash */
 	Py_TYPE(self)->tp_free(self);
 	return;
 }