October 17, On this date in 1934, Shoghi Effendi wrote not "to substitute the plural pronoun for the singular in prayers worded in the singular" and "to inform the friends to strictly adhere to the text of the Holy Writings, and not to deviate even a hair-breadth from what has been revealed by the Holy Pen."

October 17, On this date in 1934, Shoghi Effendi wrote not "to substitute the plural pronoun for the singular in prayers worded in the singular" and "to inform the friends to strictly adhere to the text of the Holy Writings, and not to deviate even a hair-breadth from what has been revealed by the Holy Pen."

1496. Strictly Adhere to the Text of the Holy Writings
"In regard to your question as to whether it is permissible to substitute the plural pronoun for the singular in prayers worded in the singular, the Guardian would strongly urge your N.S.A. to inform the friends to strictly adhere to the text of the Holy Writings, and not to deviate even a hair-breadth from what has been revealed by the Holy Pen. Besides, it should be noted that congregational prayer has been discouraged by Bahá'u'lláh, and that it is allowed only in the case of the prayer for the dead."
(From a letter written on behalf of Shoghi Effendi to the National Spiritual Assembly of Australia and New Zealand, October 17, 1934)

Also here...

17 October 1934 [National Spiritual Assembly]
Dear Bahá'í friend,
I am directed by the Guardian to acknowledge the receipt of your letter dated August 31st with its most interesting enclosures, all of which he has carefully read and considered. It is with deep gratification that he follows the progress and extension of the work of your NSA, and he hopes and prays that through the confirmations of the Almighty it will serve to give an increasing impetus to the progress of the Faith in your land.
The Guardian has read with particular interest the minutes of the meetings of your N.S.A. He hopes to receive them regularly, and thus to be in close and constant touch with your national activities.
In regard to your question as to whether it is permissible to substitute the plural pronoun for the singular in prayers worded in the singular, the Guardian would strongly urge your N.S.A. to inform the friends to strictly adhere to the text of the Holy Writings, and not to deviate even a hair-breadth from what has been revealed by the Holy Pen. Besides, it should be noted that congregational prayer has been discouraged by Bahá'u'lláh, and that it is allowed only in the case of the prayer for the dead.
Concerning the Healing Prayer, the Guardian wishes me to inform you that there is no special ruling for its recital. The believer is free to recite it as many times and in the way he wishes. There are also no obligatory prayers for the Fast. But there are some specific ones revealed by Bahá'u'lláh for that purpose.
As to the instructions given in the little black covered Prayer Book, they are by no means complete and are only tentative. When the Book of Aqdas is published, the believers will have then full and authoritative prescriptions about the form of prayer, and other instructions and rulings of a spiritual character.
With loving greetings to you and to the members of the N.S.A., Yours in His Service, H. Rabbani.
Dearly beloved co-worker:
My constant prayers for the extension of the activities in which you and your dear fellow-labourers are so strenuously engaged will be offered on your behalf that the splendid era which you have inaugurated may redound to the glory and honour of the Most Great Name. I am truly proud of the manner in which my loved friends in Australia and New Zealand have arisen to discharge their sacred and pressing responsibilities. Great triumphs, I feel convinced, are in store for them if they persevere in their mighty task. May the Almighty bless their high endeavours and enable them to achieve His purpose.
Your true brother, Shoghi.