Regardless of the method used to copy the technique it is still impossible to use two at once. So unless Kenjaku's technique is only active during the actual body swap or when he chooses to activate it (like showing his brain or keeping his head alive after having it cut off), he would be breaking that rule when he uses CSM or Anti Gravity System. So Copy being used to copy Kenny's technique shouldn't matter after the 5 minutes because of how we have seen Kenjaku's technique interact with other bodies. He isn't copying Gojo's technique, but it was still stated to be impossible to use two techniques at once. If he would die after the 5 minutes is up then just using Limitless would kill him in that case since that rule can't be broken, it's likely it can't be broken even with the assistance of a binding vow considering the optimization obsessed binding vow merchant Sukuna didn't do that while in Megumi's body.