Rules are meant to be followed always and not to be flouted according to the personal preferences or inconvenience of any individual to whom the rules are applicable. Why the Management of the particular PSU restricts the application for outside alternative employment for the purpose of onward transmission with their NOC in a year? Only for the simultaneous reasons of reducing their own attrition rate as well as non-curtailment of better employment opportunity to their own qualified employees. Therefore, such a restriction seems reasonable to me.
Well, if a real situation arises, of course, by chance only and the external employment opportunity is a so significant one as to ensure better career development and higher compensation package to the aspirant, he should be prepared to face the consequences arising out of violation of the rule depending upon the readiness of the prospective employer not to insist on the through proper channel application as well as NOC and the certainty of a new berth.