Hello,
I have been pondering about this issue since RCT2 came out, either the game is so well developed they prevented most hacking techniques, or I must be doing something wrong. In the original RCT game, there was a trainer called "Dragon AIO" Trainer, which had Ride Editing feature so you can change (EG: Trains, Cars, Chain, Speed, Type, Car Type, etc). The interesting thing about this one is, the Train/Car editing worked flawlessly in this game. I could create 24 Car Length Train for Monorails, Coasters, Railroad, etc.
In this game, I have tried Beast Trainer, and 8 Cars Per Trainer. You cannot change the Train/Car lengths amount at all, if you do, they appear changed, but when the ride is opened they reset to the last setting/max possible setting? Any idea how this can be resolved?