Hello aspirant 

Thanks for asking this question .I understood your concerns but I am sorry to say that in cbse board once you have given your 12th boards and passed them too it isn't possible to repeat that in any cost .But in case you are from state boards the rules and regulations can vary from one state to another.

Also mcc guidelines tell us that for NEET you need to pass 12th with biology , hence you can't give NEET.

All the best