Hello ristesh bansal.Answering your question-

It is totally okay to change your stream from science to commerce after 12th. Firstly, BCom is the undergraduate course that enables you to get best graduation degree after regular study of 3 years. ... And still today, it is a favourite among commerce stream students!

Science students will find no difficulty in BBA degree because it is a very basic & generic degree designed for students of all streams. ... these subjects knowledge will help you in future while studying BBA and MBA . You can take admission for BBA after 12th.

Hope you got your answer.