I did my 12th from PCM and passed from Cbse and now i want to appear again for 12th and include bio .Can l give it from regional board as private candidate? Is it legal? Am I elgibile to write NEET after that ?
Recommended: Join NEET Crash Course to Improve Your Preparation Level & Strengthen Most Asked Concepts in NEET Start Now
Your question is very conflicting as you are yourself stating that you have already passed your class XII from CBSE and yet you want Biology to be your additional subject that too from CBSE, but that's not possible as you have already completed class XII and there is no place for you to choose Biology as optional as you didn't have the same in class XII and domain change in terms of Biology stream is not possible if one has completed class XII already.
Now you can go for NIOS and you can opt for ODES, On demand examination. This mode allows you to appear for senior secondary examination after passing your 12th to upgrade your knowledge.
However you won't be provided the transfer cum migration certificate. You'll be given the marksheet only.
I hope my answer helps. All the very best for your future endeavors!