Jaswanth, you can change your marks during the correction window.Login to the official website: ntaneet.nic.in with your NEET registration number and Password. Now click on " Correction in NEET application form" and make the desired changes to your application form. But if you have already used the correction window, we would suggest you to leave it the same way because your 12th marks only determine your eligibility for your 12th but do not effect the merit list in NEET. And during the document verification, because you will show your original documents, you will be fine.