I read something some time ago about a related issue, regarding Anglican orders. Unfortunately, I do not remember where I found it, but it was written in the 1980’s when some misinterpreted a comment by a British Cardinal that Anglican orders might become valid.
According to the essay, the precise reason why Leo XIII declared the Anglican Orders invalid was that there was a defect of form and intention. In other words, Bishops using the new rite had no intention of conferring Holy Orders as understood by the Universal Church, but instead had a “native character and spirit.” The defect of form followed this intent by deliberately striking out those words that clearly conveyed the Catholic intent. Even later changes to the rite (including one that expressly refers to the power to forgive sins), were made in vain, because the intent was still lacking.
However, the “author” of the Anglican rite is not an individual or even a group of individuals. It is the Anglican Church. In theory, then, the Anglican Church could declare, without changing a single word of its rite, that it interprets and intends it to do what the Catholic Church intends, and not something else. The rite would then be valid (prospectively, and only by a validly ordained bishop).
An interesting theory, which has application to Donald’s problem. When Paul VI “changed” the rite, unlike the Anglicans, he did not intend to change the intent of the words, that is, to create a Catholic priest/bishop with the ability to absolve sins, confect the Eucharist, and do other functions proper to that state. (Apparently, the new rite also conforms to Pius XII’s requirements, which I must confess I have not read.) Thus, the new rite is valid, because both the intent of the ordaining Bishop and its manifestation in the prayer of ordination express the intent to confer Holy Orders as they are understood by the Church.
Hope these thoughts, which are similar to those in other posts, are helpful.
-Illini