Wait a sec! I'm a bit confused now. What is it that you are talking about - an underrotation or a prerotation?
I believe that these are two different things scoring wise. "Under", which is determined based solely (unless the rules have changed... Have they?

) on the jump exit is punished by reduced point value. "Pre", which is screwed (literally) jump entry, is just as legit as any other entry under IJS and is merely a disputable jumping technique that is not punished anyhow (except by an edge call when it causes a flutz).
Or, have the rules changed already? How can I not know

Bring me the link!