You can, but are they for the same subject/similar courses in the same department? I think most departments will allow you to swap from a MSci to a BSc after you get in during your first year or even after, depending on the uni (you can swap from BSc to MSci too, but apparently that’s harder) or switch between courses within the same department if you’re unsure currently. I’d advise you not to waste your choices by putting very similar courses at the same uni and put another uni instead.