Small Engines (Lawn Mowers, etc.): hydrostat lawnmower, pully, lawnmower

Question
I was wondering, i know how to speed up a regular lawnmower, bigger front pully and smaller back depending how fast you wish to go but how does it work with hydrostat do we do the same to speed up the pump or is there anyway i can accomplish this. I would probably want to keep the one on the rear end the same anyway because of the fan on top of the tranny but will this work. thanks

Answer
Never thought of it before, because I never modify mowers I just
repair them to perform the way they were designed, don't have time
for experimenting.  The only way that comes to mind would be a bigger engine pulley, but how much more without doing damage, I don't
know.