I don't know in which standard you are in but yeah! the subjects can be replaced but you need to know if you institution allows it. I would recommend you to repost the question more elaborately (provide which course you are studying), so that we can understand and provide you all the information required as soon as possible.

Goodnight :-)

Hey!

You haven't mentioned where computer science can be added instead of physics. You will have to mention exactly about what you are referring to. For instance, if you are taking a merit based admission, then one is required to write best four or best five subjects. If you want to know the eligibility of that and the subjects that can be added, the you will have to mention the name of the university or college. You may mention these details in the comment section so that it can be answered accordingly.