"Do a little wrong?" (on taking it upon yourself to fix faulty translations)

Ed Peters writes about a priest who decided to change the translation of pro multis long before the Vatican had issued its decision:

Obviously thoughtful and desirous of bringing sound liturgy to his people, [a priest] wrote that, with a smattering of Latin and some input from those who knew more, he had long ago substituted "for the many" in place of "for all" when he celebrated Mass. He justifies his action on the grounds that "for all" was clearly wrong and that people deserve a correct translation of the Mass. He added that, if his bishop were to direct him to stop the practice, he would do so immediately.

I think this approach is quite wrong. [Find out why...]