According to the Tzitz Eliezer, is transgenderism actually muttar?

If I am understanding everything correctly. The Tzitz Eliezer’s psak is that if a man get’s a surgery that alters his genitals to that of a woman, they assume the halachic status of a woman, and are mechayev to all the mitzvos specific to women (tznius, shabbos candles, etc). And furthermore, this action according to him does not violate the posuk וּמָע֤וּךְ וְכָתוּת֙ וְנָת֣וּק וְכָר֔וּת לֹ֥א תַקְרִ֖יבוּ לַֽיהֹוָ֑ה וּֽבְאַרְצְכֶ֖ם לֹ֥א תַעֲשֽׂוּ׃ because such a person assumedly would have undergone hormone treatments that would have already rendered them impotent by the time of the surgery, meaning that this operation could not at that point be considered castration.

Two questions: One, am I misunderstanding something about this psak? And two, even holding by this psak is undergoing such a process muttar given that it would probably prevent a person from P’ru ur’vu?