Regarding this post, it was pointed out to me that R. Shalom Carmy's article does not say that Rav Soloveitchik did not change his mind about "Da'as Torah." Rather, it says that one can read the texts without being forced to say that he changed his view. Therefore, whatever change he may have made, if any, need not have been radical.
R. Nati Helfgot directed me to the following passage in an essay by R. Aharon Lichtenstein (Leaves of Faith, vol. 1 pp. 227-228:
True, he did not, in the long run, hold aloft the banner of the ideology that is now termed "Da'at Torah," which maintains that every political question has an essentially halakhic character, and is thus susceptible to the obligatory and exclusive decisions of the gedolei Torah. At first he inclined to this view, and even asserted it with enthusiasm. As he said, in his eulogy for R. Hayim Ozer ז"ל...Also of relevance is the following passage from R. Hershel Schachter's recent article (p. 4):
After a time, he abandoned this view, and in the course of decades he accepted and even sharpened the distinction between matters involving mizvot (divrei mitzvah), which are to be decided by halakhic decision-makers, and other matters (divrei reshut), in which significant weight is attached to the opinions and authority of other leaders, or to private judgment. Nevertheless, although he rejected the decisive reach of rabbinic authority in political matters, he was insistent that such matters be determined from a perspective of refined spirituality and in consonance with Torah values. And he fully recognized that he was one of the few who could bring the proper measure of spirituality to bear upon Religious Zionism so as to ensure its standing as a Torah movement.
We also heard similarly regarding political matters, that many times R. Chaim [Soloveitchik] reached a decision and did not allow other rabbis to vote and disagree with him. This is in accord with the aforementioned view of the Vilna Gaon, that these Torah giants believed that they had succeeded in achieving an absolute conclusion from which there is no room to deviate right or left. However, our teacher [R. Joseph B. Soloveitchik] frequently said -- many times -- that he does not say "Accept my view." He would say this regarding both halakhic and political matters.
I heard from R. Norman Lamm that our teacher was once asked about a political matter, and the rabbi responded to the questioner on the issue. The questioner then asked, "Is our teacher's 'Da'as Torah' such-and-such?" Our teacher immediately responded, "I did not say 'Da'as Torah.' I only said my opinion and the listener will choose." It seems to me that his words mean as follows: People tend to use the phrase "Da'as Torah" as meaning an absolute conclusion from which the listener has no permission to discuss or disagree. This was not the approach of our teacher, as is famous and known to all.