B.Com

Hello Reema,
BCA and B.Com have a very vast difference so it depends on the college and if you have both the courses in your college and college is ready to change the course then only you can get a chance so please try to contact to your college.

49% is a bit low, but I think you should send an email to the Australian universities.

Yes, you can apply to most of the government jobs. All the banking opportunities are open as you have done your education in finance.
You may also apply to oil and gas companies.
Generally, these companies do not recruit through walk-ins and have national level tests followed by an interview.
All the best.

Firstly, I would like to tell you why you want to drop because B.Com is not a high degree so with B.Com you can do company secretary and concentrate more on company secretary because a good portion of B.Com depends upon the syllabus of Company Secretary course so my suggestion is that continue your degree course while doing CS.

General eligibility is that a candidate should hold a degree from any of the recognised universities or must have an equivalent qualification so any graduate can appear for this exam.

You have to complete 10+2 with 50% marks. But, sometimes with below 50% marks, you may get opportunities, if seats are available.