In our organization tests up to Nikyu are based on a list of techniques known to the student before hand.
Ikyu and Shodan have a combo of listed techniques and others where it might be any 5 techniques against a specific attack plus a jiyu waza session or two.
Nidan and above it is pretty much entirely semi freestlye where we will be asked to do anything from any attack or sometimes a specific technique from any attack plus jiyu waza.
It seems like you could pre decide what you will do for the free form stuff but having done these tests up to Nidan I can say you may think you have a plan but since the attacker can choose how he attacks and you don't know what that will be and he will be coming at you pretty hard it falls apart quick. You soon end up letting your self do whatever feels right. That is why you see a person doing 5 minutes of shihonage and you think "doesn't he know anything else?"
I know during my Nidan test I at times was telling myself I gotta show something besides Iriminage but by the time the thought formed another attack came in and I had to deal with it.
If it looks like a person moves smoothly from one thing to the next it probably means they have been able to keep their mental calm which is likely one of the items looked for by the tester.
I like the idea of freestlye testing and unless you are able to plan ahead of time with your uke what you will do I think it will end up being spontaneous whether you started out witha script or not.
Thats been my experience and having witnessed a lot of Yudansha tests I think most of them had to move to the beat too.