Ahh, but see, here is the stickler: the poison pill is already eaten. It matters not if the Roman church declares the forgeries herein, for the poison was already ingested in the form of Gratian and Aquinas. Have they been discredited by their reliance upon these forgeries? No, of course they have not. And so it goes.
Take Gratians Decretum. Despite being the standard textbook for students of canon law during the Middle Ages, the Decretum was never recognized by the Church --- by a Council or by a Pope --- as an official collection. It was a practical and continuously modified compendium of principles, maxims, examples, arguments, and case law.
Interestingly, many auctoritates (dodgy quotes from popes, for instance) were inserted in the "Decretum" by authors of a later date, not always as original sources, but often as makeweights and examples.
Over time, the Decretum developed different versions, layered up with cases and commentaries --- a Talmud-like process --- until after a millennium it eventually comprised some 10,000 norms. These became impossible to reconcile with one another due to changes in circumstances across different countries and centuries.
In other words, Gratian's Decretum was not irreformable dogma (in the strict theological sense). It was case law and commentary. This whole ball 'o wax was made defunct by the very buttoned-up and simplified Code of Canon Law (1917) which replaced it, and the next revision of Canon Law (1983) which replaced that.
Was the whole project permanently or fatally poisoned by having Pseudo-Isidore as one of its sources 1200 years ago? I dont think so. < P> Heres what I think: the mid-800s AD were a desperate time: the Holy Roman Empire was disintegrating while the Vikings tore bloody chunks out of Christendom to the north, the Muslims to the south. Good popes and bishops were struggling to preserve the structure and security of the West, the Church and its people. In this very dark time --- here Im using Warren Carrolls words --- the Papacy had been brought, though unwittingly, to the employment of falsified elements of canon law. They believed it to be legitimate --- much of Gratian's collection was legitimate --- and they needed settled norms in a time of chaos.
I think its a huge, painful tragedy that a handful of Frankish monks appealing to the pope to restore their deposed bishop, used a successful ruse to get forgeries inserted into canon law. A Bad Thing. It indisputably led to long-lasting distortions in Western papal jurisdictional claims. But is it irreparable? No.
Ecclesia semper reformanda. Don't leave the field of struggle too soon. The Holy Spirit is still Lord and Giver of Life, and Christ still King.