Hey,

According to the rule you Will have to retake the exams for all the subjects as per the syllabus. But the practical marks will remain same.

Coming to your next question the answer

You need to apply as private candidate so no need to get re-admission in school . If you want to change school you can also do this. You have one more option that is you can also opt for NIOS board.

Hope it helps.

Good luck.