May one immerse in hot Mikva on Shabbos when needed and rely on Korban Nessanel.

Talmud (Shabbos 39b) and Shulchan Aruch (O.H. 326: 1) maintain that one should not wash the body with hot water during Shabbos, even when the water was warmed before Shabbos to avoid coming to warm the water on Shabbos. Mishna Berura (ibid 7) rules that when immersing in a Mikva during Shabbos the water should only be lukewarm. He does quote also the Korban Nessanel without mentioning his lenient ruling. However, in Shaarei Tzion (5) he rules that in need one can relay on him. Hacham Tzvi permits this Tevila during Bein Hashmoshos. Some Chassidic groups that immerse in the Mikva daily before davening are lenient to do so during Shabbos also even when the water is still warm.