In this recent question we looked at the following sentence from the apostolic constitution Provida Mater Ecclesia:
§ 2. Instituta, salvis communibus iuris canonici normis quae ipsa respiciant, tamquam proprio iure, peculiari eorum naturae et conditioni arctius respondent his praescriptis reguntur :
[…]
2° Normis quas Sacra Congregatio de Religiosis, prout necessitas ferat atque experientia suffragetur, sive Constitutionem Apostolicam interpretando sive ipsam perficiendo atque applicando pro omnibus vel pro aliquibus ex bis Institutis edere censuerit;
Or, boiled down to (what I think are) the essential parts:
Instituta reguntur normis quas Congregatio, prout necessitas ferat, edere censuerit.
I do not understand the subjunctive mood. Why is censuerit in the perfect subjunctive, why are ferat and suffragetur in the present subjunctive?