In the case of res judicata, the matter cannot be raised again, either in the same court or in a different court. A court will use res judicata to deny reconsideration of a matter.
The doctrine of res judicata is a method of preventing injustice to the parties of a case supposedly finished, but perhaps also or mostly a way of avoiding unnecessary waste of resources in the court system. Res judicata does not merely prevent future judgments from contradicting earlier ones, but also prevents litigants from multiplying judgments, and confusion.
Since respondent No.1 obtained appointment on the basis of bogus certificates, in our considered view, the principle of res judicata will not be attracted to the case on hand
What you say has not been proved before court, at least as per the opinion and judgment delivered by CAT.
The high court will not go beyond the findings of CAT to some extent until and unless there is a gross violation of law of land.
You may file a petition with a different cause of action which is not relevant to this settled case, is there any loop hole to approach court from a different angle ?