Yes, you can take an additional subject in ICSE/ISC to try and boost your percentage. Boards usually allow extra subjects, but only part of the marks may count toward your overall score. Your previous attempts won’t invalidate this, as only the best attempt is considered. You must register through your school for the 2026 exam. Make sure to check the official ICSE/ISC rules for eligibility and mark calculation. This way, improving to 75% is possible if the extra subject marks are enough.