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/gameengine/GameLogic/SCA_MouseSensor.cpp

@@ -311,16 +311,15 @@ PyTypeObject SCA_MouseSensor::Type = {
 	0,
 	0,
 	py_base_repr,
-	0,0,0,0,0,0,
-	NULL, //py_base_getattro,
-	NULL, //py_base_setattro,
-	0,
+	0,0,0,0,0,0,0,0,0,
 	Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE,
 	0,0,0,0,0,0,0,
 	Methods,
 	0,
 	0,
-	&SCA_ISensor::Type
+	&SCA_ISensor::Type,
+	0,0,0,0,0,0,
+	py_base_new
 };
 
 PyMethodDef SCA_MouseSensor::Methods[] = {