Hi there Vishwa!

CBSE offers improvement exams so that the students can take one more shot at the exams improving their grades. If you get an improved score than from last year, surely that marks will be considered as your plus two marks. If you improved a subject and got less mark than the previous exam, don't worry you will get the previous mark. Your last part of the question is not clear! eventhough if you are meaning that the marks obtained from the improvement exam can be considered your final marks and entering it, that would be an 'YES'