It's easy if you're on PC. If you're on console, then there's nothing you can do about it unfortunately, unless they release a small patch.
If you are on PC then what you have to do is:
- Open the Database.xml file in the root F1 2012 folder, with Ryders Database editor,
- Then scroll down the left side until you find "track_model".
- Then scroll to the right, until you find the categories "option_tyre" and "prime_tyre"
1 = Supersoft
2 = Soft
3 = Medium
4 = Hard
Then (for Austin) change the option to "3" and the Prime to "4"
then save, and you're set.
Hope it helps.
They're also using Medium and Hard for Brazil next weekend as well, so you might want to change those values as well.