Well I didn't really, could double check it later. I always take extra notes when I add any car, serial numbers is something I triple check before I launch the game.
It might be possible to do in other games contemporary to HS with support for ghost files.
Yes, at least NFS3 has a similar setup. Editing those files is just as simple as it is for NFS4 (not everything is in the same order though).
There's not much left to cover in the gst files. Mostly are unknown to me and some of them maybe doesn't even lead to anything. But here's something:0000119C, 000011A0, 000011A4, 000011A8
000011AC, 000011B0, 000011B4
These addresses is the Car Tuning
you've done to the selected car. Default value: 00 00 80 3F
(middle on the slider).
Don't know exactly what the min and max values are for them at the moment.
I'll revisit the first post to make it look better, at some point.