I did the four week BSS3 rotation and I didn't do the step aerobics on an incline. There's no way that step aerobics at an incline makes sense for my body (5'3" with tight calves). I tried it once and didn't like the stress that the incline put on my achilles or how high I was forced to step at a fast pace. I did all of the step aerobics with the box flat and only inclined it when they did medium or slow paced lunges and such.
I didn't do the abs on the box either. Again, I tried it once and hated how it felt. I did all of the abs on the floor and put my hands, palms down, under my lower back for reverse curls, like i always do.
Just modify the moves you don't like. Nobody is going to hate you for it.