nomination in gratuity is changeable by submitting the form. however at the time of filing the form F the employee has to nominate one or several persons to get claim of the amount .
Naturally for an unmarried employee the parents ( father/ mother) is nominee, and for a married employee, simple way the 1st nominee is spouse,
such clause arise when the employee seeks to nominate any person out of "family" orbit, and in such situation, the employee has to clarify that why he / she is doing it, so that the payment authority would not get trouble in court of succession.