Is it possible to do this, considering it’s not that big of a switch between fields/focuses? I know you can go on the portal and request for a major change,but I feel it’s risky and they might reject my app after I do that… any tips?
You might want to check with the Biological sciences department and ask how many students have successfully changed majors over the last few years. This will help you gauge the possibility especially if the change is dependent upon you from enrolling at UCI.
I got into the pharmaceutical sciences as well 
Got into pharmaceutical sciences too! 