I was wondering whether it's possible to change out the transmission on Audis to make a Tiptronic into a manual, or the other way around.

I imagine it would be theoretically possible but would involve MAJOR comprehensive changes. Everything from the ECU, the transmission, and g-d knows what else. You'd be rebuilding the car.

So if you're looking to see if its possible to do a simple swap, the answer is no. It would be cheaper to just sell/trade in your S4 for one with the alternative tranny.

its POSSIBLE.... cost effective and worth it, most likely not....