totally agree,dont do cs with the intention of getting into law firms.with the help of cs degree it will be easier for people to gain knowledge of m&a,ibc,dt and idt,sebi rules and regulations.
you will get sufficient knowledge about aforementioned subjects.
it might help you to get into law firm interviews,but be prepared for technical questions ,thorough research is what required for getting into law firms in any verticals .

For finance, the best way would be to undertake research and publish papers/articles/present in conferences. It builds your resume in that direction, and if you ultimately seek a non-law position in an investment bank/PE/VC/consulting/financial research, the current job market looks very favourably for research experience. Try building your profile to showcase some empirical or quantitative work, and you can also do a research assistantship under a professor.
For a law position, read contract law, transfer of property, bankruptcy, understand project financing, bank transactions, lending agreements, financial regulation. You can try doing corporate law moots, however I find publishing slightly more flexible and suited to my interests. Intern aggressively and seek out guidance from lawyers in investment banks and multinationals. If you can, then a commercial litigation internship with a well-regarded counsel (who deals with matters in banking law, commercial disputes, bankruptcy, etc.) either in Bom HC or at the SC for a couple of months would be a game changer. The amount of perspective you gain from the right litigating lawyer is immense, eg Shyam Divan who deals a lot with such matters apart from constitutional litigation.
An international experience in the form of a position at a research centre would also be very helpful, but it is hard to break in. If based in Bangalore, then think of working with professors at NLS or IIM Bangalore - build a rapport and do work for them, and maybe you can ask for a reference for commercial oriented work, or research (whatever interests you).
Dont get bogged down by the usual law school activities, but always always maintain a high CGPA, the financial sector still is notorious for selection only on the basis of marks. Remember that you can earn multiples of what corporate lawyers earn if you are able to crack the finance industry.

While CS as degree was not very helpful in getting me my law firm job, the stuff I learnt from the course was surely quite helpful. CS is not a very easy course, one has to cram a lot of unnecessary things word by word to be able to pass at least the final exam. There were times when I'd feel I could have instead done better things than mugging up all that unnecessary infomation. All in all, I don't discourage law students from taking up the course, but only do it for the knowledge. Face value of a CS degree isn't much.

Hey!
I appeared for cseet after my 3rd sem and cleared it with less than 2 weeks of prep. Planned to give executive right now but opted out, ater paying the fee and giving the pre-exam tests.
CS is a good option but it wont exponentially increase your chances of getting a job, at least that is what a senor told me. I was concerned that appearing for CS and doing the articleship and other training and orienaion modules, just for an added edge will affect other things that i am expected to do: internships. Even this month for instance, if I were to appear, it would have clashed with my internship. So, i put it on hold for now.
It may help you but considering my college where placements and T1 internships are given based on academics(MAJORLY), having CS would not have helped much anyway so I was advised to give it up for now, and focus on being in the cream of the batch.
But again, there's no rule that fits all. So think it through and you do you. All the best!