Re: In the moment....transitioning into another technique
When you train to drive a circle, your instructor won't give you a square pattern. If uke gives you a square tell him for now you want a circle from him.
Following your basic understanding of driving a circle, square or whatever shape, then he puts you on a normal road. That's when you do what ever is acceptable ie circle square etc. Uke can give whatever shape to you and all you have to do is fit something into that shape. You could like most toddlers try to bash a square into a round hole, or you could be more successful, if you use the appropriate shape instead.
Similarly, you're trying to learn the form of ikkyo, nikkyo etc from attack type a, b, c or d... then you have to do that form regardless. Once you know the form, the teacher can have his students attack you with whatever, now you do whatever is natural.