Looting code is rarely possible for that as the approaches of the scripts for map generation vary a lot.I've seen map scripts with all those sorts of things. I believe it was SmartMap. That one had like almost every aspect configurable. Maybe you can loot it to add to other more popular map scripts?
I don't care for massive oceans (pita for wars) so I always use PlanetGenerator that lets me lower ocean %.
Btw, I have added a sea level option to PerfectMongoose some time ago that causes more or less ocean size.