Can I change my major?

I have gotten an offer from the medical sciences department at UCL, but I know now that I want to shift to biochemical engineering. My predicted grades are 5A*s in math, chemistry, physics, bio, and IPQ, and I'm sure I will get these grades. How likely or unlikely is it that I can transfer to biochemical engineering within the first month or two of joining UCL?

You know, you can email the UCL's admissions department right now and ask if you can transfer, even before the course has begun? No guarantee that it'll happen but still worth a short

I did! Unfortunately, they told me that they already closed admissions for biochemical engineering but that I can transfer in the first month of university ☹️ However, it seems that I shouldn't risk it since it's unlikely that I will be able to shift