By the Grace of G-d 8th of Shevat, 5725 Brooklyn, N. Y.
Greeting and Blessing:
This is in reply to your letter of January 7th.
There seems to have been a misunderstanding with regard to the information that you were given relating to the Nussach of prayer as well as the manner of putting on Tefillin. Generally, all matters of Torah and Mitzvoth cannot be affected by the Mitzvo of Kibbud-Av. Particularly in this case it is quite out of place, inasmuch as you write that the father not only has no objections, but on the contrary, is very pleased by the change.
It has been explained in various sources that it is not proper to change from Nussach Ari to any other Nussach, for various reasons.1
No doubt you will observe the Yahrzeit-Hilulo on the 10th of Shevat, and may you derive lasting inspiration from this occasion.
With blessing
By Nissan Mindel
Notes and sources
1) Shu"t Maharashdam, Orach Chayim, 35; Divrei Chaim, vol. 2, Siman 8; Shu"t Beis HaYotzer 8; Minchas Elazer, vol. 1, Siman 11.
Source: Photocopy of original
Published: Letters From the Rebbe, Vol 3 (OSL, 1998), 97.