A gentleman who complained to the Rebbe in 5709 that this line was removed purposely by Kehos was told by the Rebbe the story of the forgery. The Kfar Chabad reporter found a handful of private people who have the first edition of the Piskei Dinim with the correct line, all public Jewish libraries have the forgery in their version.
Professor Shmuel Glick, director of the Schocken Institute for Jewish Research of Jewish Theological Seminary in Jerusalem, and associate of the Schechter Institute, seems to take issue with this letter of the Rebbe. The last portion of the article is dedicated to demolishing his statements and calls into question his credentials.
In his book "Kuntres HaTeshuvot HeChadash" Professor Glick states that the Rebbe's letter contains no truth, that the true version is the one praising the GRA, that Kehos perpetrated a falsehood, and quotes two frum researchers, R. Moshe Blau and R. Yehoshua Mondshein. The first he quotes from to establish that there is no other version of the first edition of the Piskei Dinim. As Kfar Chabad rightfully points out, he couldn't do the minimal research a reporter could do to find the other version? The second he quotes to establish that Chasidim would forge to protect the honor of their Rebbe.
Both of these researchers have sharp words for this Professor Glick. R. Blau for his part calls this a "blood libel on the Rebbe". R. Mondshein takes him to task for his error, his tone and misusing R. Mondshein's words to produce a falsehood.
I cannot tell if this professor is frum and merely working for Conservative institutions or himself Conservative. I feel enough respect to wish to hear his apology or defense for his error and tone, as his son served as a soldier in the IDF and died in a car accident while serving. I would assume that the professor is frum, as his son studied in Yeshivah.
UPDATE: shturem.net carried the scandal further. The original Kfar Chabad article is here, and a follow up shturem article with the professor's evasive response, neither admitting error nor apologizing. He does say he is travelling and the book is not with him. Yet he did not respond to the original request of the reporter for a comment. The comments online there are very revealing as well.
An honorable mention to Chaim Grade for old times sake. They republished a hesped for him written by Yisroel Duchman in the Algemeiner Journal, in which he talks about Grade's reconnection to Judaism through the Rebbe, to the point where he has a pithy conversation with a former Communist friend in Canada, who saw him wearing Tallis and Tefilin early one morning and exclaimed: "Chaim, you too?" "Yes, it is I..."
He quotes Chaim Grade on two subjects: his father, R. Shneur Zalman Duchman: "Reb Shneur Zalman HaLevi Duchman, author of the collection "LeShema Ozen"; a Tehilim Jew in whose every step (יעדער שריט און טריט) was heard the song: Ashrei Temimei Derech!" On the Rebbe: "Dear Rebbe, continue for many years to enlighten the world with the Torah, the good and the wisdom of yours; with your activities to bring heaven down to earth and to raise the earth to the heavens; with the song of unification of yours to "He who rides the clouds" and with the consolation to the sinner that he too has a holy spark - and whenever you pray for others, remember as well Chaim ben Velle."