Are you meeting with a SSC online or in person? I don't see a justification for substituting the rack pull. We get kyphotic lifters all of the time and if you can't set your back with the bar on the floor then you need to learn how to. That's what we are trained to teach you how to do.
As for your diet, you don't need to eat high carb necessarily but sub 100 g carbohydrate for a male lifter is too low. Try 200 g to start and keep your fat under 100 g and see what happens.What time of day did you check your testosterone?