In response to the stated question, i would adamantly argue that the Treaty of Universal Peace signed in London in 1518 was not so mucha diplomatic coup, rather fortunate opportunity which significantly advances England's prestige globally whilst also ensuring its protection. I would argue this for one main reason, a diplomatic coup would infer that Wolsey, indeed Henry VIII would then recieve enough power to not only arbirtate the european conflicts (Hapsburg vs Valois) but also Stop any wars from occuring. this is not the case, they were seen as peace arbitators, promoters of justic between the increasingly war torn Europe but a year later when Charles I became the successor to Holy Roman Emperor Maximilian, the situation changed in Europe again.
Thus, England did not have the power that a coup would usually command, and in 1522, after years of deliberation, they chose to join Charles in his war against Francis I. By now, the older Henry who had bee out shone by Francis I in 1515 (with the young successors impressive victory and capture of Milan) was now outplaced by the failure of the Treaty of London and therefore i think it is only sutiable to conclude with the words of G.R.Elton
"After 1519, England was really out of her class in this contest of heavy weights".
So, in my opinion, it wasn't a diplomatic coup, rather a stunning peice of improvised opportunitsic diplomacy on behalf of Wolsey who saw that hes master wanted to be influential once more
