You are overthinking it. Your icebreaker is not a test, other than it allows you to demonstrate that you are able to stand in front of a few other people and string a semi coherent sentence together. You will not fail your common selection board because you have not prepared the most perfect answer for an ice breaker question.
Have you practiced the answers to the questions you might be asked? Do you even know what they might be? Of course you don't because the person asking them has probably not even thought of the question yet - they will do so as they listen to your icebreaker.
Just speak as clearly and confidently as you can, and it will all go OK.
From what my ACIO told me it is exactly the same. Important to prepare, as too many at my Pre-ADSC had no idea what to say. Though don't over do it, you will end up pressuring yourself and finding yourself at blankville.
Not to say that it will be the same but when I was at Lichfield last year you don't really do your exact icebreaker, you speak about yourself for 30 secs then 1min 30secs on a random given topic (you get time to prep), just practice what you've been doing but be prepared to think on your feet.
My icebreaker was on the first night, we had a game of scherades I had done mine, the next person up was a really fit girl, she was distracting a lot of people, the DS lean over right Number 16 you need to pick a film for her to do, It was my first encounter with Emperor Mong, I whispered in her ear. She looked shocked and the DS asked her what it was, she leans over whispers to him. He starts laughing and when he got himself together gave her another film title. I had forgotten about this and on my interview panel 3 of them just hitting me with questions. Then at the end they said they will let me know when my basic training was to start. As I got up to leave the Captain in charge of the panel said, "Gentlemen on scherades do not tell girls no matter how good looking they are to do Big Country!