Along with CA articleship you can pursue one additional course that too as per guidelines (timing restrictions). Thus technically you can pursue LLB along with CA if its the only other course and you can produce a certificate in 112 from your college regarding class timings (which i think creates problem as regular LLB classes before 11 and after 5 are not common).
However if u start ca, then untill your training starts (which will be only after you pass cpt & ipcc 1st grp) you can pursue both cs & llb. if till then you are able to pass cs final then no need to inform about it, you can fill 112 for other course
There are many students who pursue additional courses without 112. Nothing will happen till you are caught. If you are caught then institute can refuse to acknowledge your articleship period or can take any other action Its your own risk.
CS & LLB is also a good combination. So just from career point of view you can continue with these two also. Be sure before taking ca, that you can manage these 3 at a time.