The SCT tuner doesn't allow you to mess with any values in the tune. . . . . .
Yes it does -- or at least mine does, I have done it, for both rear end ratio and tire size.
You go in as if you were going to load a tune; at some point it will present a screen "adjust parameters" ; select that option and then it gives a list of things that can be adjusted -- rear tire size (revs/mile) is one of them ; then youi continue to load the tune, with the adjusted parameters. So you CAN adjust for the track tires when you load the track tune.
But it still doesn't make any real difference . . .
I don't understand this talk about the 93R tune being to touchy on the throttle response. I drive that tune on the street all the time and I don't see any big issue. Maybe in autocross I'd notice, I haven't done that (yet) so I don't really know.