Yes , With NIOS marksheet you will be able to use the marksheet in any examination and the fact about 4 subjects isn't mentioned anywhere. In the official website , we can apprehend a statement: '' For obtaining a pass certificate, you are required to pass in a minimum of five subjects including one or maximum of two languages from Group 'A' and other three or four subjects from other Group. However, you are free to take upto two additional subjects. ''

I hope my answer helps you. All the very best for your future endeavors!