strawberry c

I am Hong Kong local, a personal crypto trader and currently planning to apply BNO visa. I would like to liquidate all my crypto holdings right before I entered UK so that I would not have to pay CGT upon arrival. Could the selling be done through fiat pair (BTC/USD) of the crypto exchange (which is KYCed using my HK identity) and without being withdraw from exchange to my own bank account? So that upon arrival using my approved BNO visa, I could buy back the crypto easier without sending fiat from bank to exchange again. Also I would like to know from which dates do I need to keep my transaction records on the exchanges for better preparation for tax report once I become tax resident using BNO visa.