In case anybody wonders where his car went.. Another youtuber bought it, and now it's available for daily rent.
https://turo.com/rentals/cars/fl/oviedo/ford-shelby-gt350/327600?s=2TpsExAj
Correct, the FP (and most other tunes) will push you out of ST due to the boost increases.
However, if you've never autocrossed before, just show up and have fun. Most regions have some kind of "novice" group for new guys anyway. And you'll have a ton of fun regardless of class.