The dive planes animation is a Hard coded thing, yes.
You can add a 3rd dive plane to the forward or rear planes.
The controller only looks for the number of planes.
It does not restrict that number as far as I recall.
(I could be wrong! And alot of times I am!)
BUT!
Once the Sub levels?
Up go the planes!
If the Planes rotate to a Surface position?
So would the Gun.
Now, the water transition and water interaction controllers.
Water interaction only happens once.
Water Transition happens every time the controller meets it's settings.
Some SH3 mods that do the water drain effect had to use work arounds because Water Transition is only in SH4.
(Well probably SH5 also but that's another can of worms!)
Water Transition can be linked to anything you want.
Not just a particals effect.
It's a controller that says when to start and under what conditions.
The particles only stop because THEY are set to stop.
The controller is not telling them to stop.
Only when to START!