When a person came up with the idea of writing out the Tanya for a holy effect, the Rebbe called it a “waste of valuable time” and gave guidelines for which segulos are appropriate.
Since the Tanya is considered the “Torah shebichsav” of Chassidus, one sincere chossid thought that it would be appropriate to write out the entire Tanya in his own handwriting, in the spirit of the mitzva of writing a sefer Torah.
Although this was before the nesius, the Rebbe’s opinion on the matter was sought, and the Rebbe shared his thoughts in a letter dated 11 Adar 5708 (1948).
The Rebbe began by differentiating between a rational systematic avoda, such as breaking a negative trait through taking the opposite extreme, and an avoda using segula powers, like reaching a higher level in learning through distributing tzedaka.
“Regarding a rational avoda,” wrote the Rebbe, “everyone is obligated to search and find personal solutions that will work for him. However, with respect to segulos, whatever the Rebbeim have not told us, we cannot know. Therefore, there is no room for creative thinking…”
In conclusion, the Rebbe addressed the misjudgment of this particular suggestion: “Unless this is a person who will be inspired by the experience of writing out the Tanya, then this is a waste of his valuable time. He could use the time to actually learn the Tanya instead. And writing instead of learning is like a fine diamond cutter consuming his time with menial tasks.”
(Igros Kodesh, Vol. 2, Page 343)