Use a text editor to edit the "options.txt" file in the "c:\documents and settings\\application data\atari\rct3 " folder. This folder is "hidden" by default, so you will have to enable Windows to view hidden files and folders. Add the following lines to that file. You may have to restart a scenario for the changes to take effect.

GuestsHaveFixedHealth 1
GuestsIgnoreRideIntensity 1
GuestsIgnoreRideNausea 1
GuestsIgnoreRideCost 1
GuestsRevisitRides 1
GuestsRideUnratedRides 1