I don't know how any traditionalist can dance around this anymore. Let this sink in: "unblemished by any error" Now either words don't mean anything when the Church speaks from a Pontifically approved Council or PF is not the pope. It has come down to black and white.
Very simply, like Fr. Kramer, it seems that most sedes take the whole thing entirely out of context, which is of course necessary to do in order to maintain the various different flavors of sedesim.
1) Taken in context of the section; "On the infallible teaching authority of the Roman pontiff", we find this section you quoted is where they are teaching
strictly about when the pope speaks ex cathedra - if however, it is as you allude to, then you must admit that you actually believe the pope is himself a god, personally always infallible, which is the only way he could hope to never make "any error" - but that is not at all what they are saying.
"For the holy Spirit was promised to the successors of Peter, not so that they might, by his revelation, make known some new doctrine, but that, by his assistance, they might religiously guard and faithfully expound the revelation or deposit of faith transmitted by the apostles...
...Therefore, faithfully adhering to the tradition received from the beginning of the christian faith, to the glory of God our saviour, for the exaltation of the catholic religion and for the salvation of the christian people, with the approval of the sacred council, we teach and define as a divinely revealed dogma that when the Roman pontiff speaks Ex Cathedra, that is, when, in the exercise of his office as shepherd and teacher of all Christians, in virtue of his supreme apostolic authority, he defines a doctrine concerning faith or morals to be held by the whole church, he possesses, by the divine assistance promised to him in blessed Peter, that infallibility which the divine Redeemer willed his church to enjoy in defining doctrine concerning faith or morals."
2) The decree states infallibly that the Holy Ghost's assistance is not employed when it comes to new doctrines, what it does *not* state, is that it is impossible for the pope to preach new doctrines, that is, except when he actually solemnly
"defines a doctrine..." etc., and it also does *not* state that the pope vacates his office if or when he does preach new doctrines.