Hello aspirant,

There is nothing called legal or illegal in studying. You can study as much as you want and whatever you want because it depends on you ultimately if you can simultaneously study two courses together. The timelines of both the courses might crash sometimes so you will have to take care of that.

But if you are doing HS from different stream, the thing is to remember that you cannot show your both the certificate in a same place, you must have to terminate one. And if you have showed recently HS certificate, some might ask for GAP certificate also as there creates gap of 2-4 years from 10th to your new HS certificate.

Hope it helps you..

Best of luck..