#809: Not Nonchalant on a Name Change
Shinui hashem (changing a person's [Jewish] name) is not done lightly. A person’s name is a tzinor hachayim (channel of life) for the individual. The pasuk (verse) in Bereishis states, “nefesh chaya hu shemo” (a living creature, this is his name); this is interpreted to mean that the life-giving nefesh (also called neshamah) is bound with the individual’s name. It is further taught in the name of the Arizal (16th century kabbalist) that the name the parents give their son at his bris is chosen b'ruach haKodesh (Divine inspiration).
There is a tradition that shinui hashem can remove a gzar din (negative Heavenly decree) from a person. There are two explanations for how a name change can affect this. The Midrash says that the shinui hashem of Avram to Avraham was associated with the mazal (destiny) of the different names: Avram was childless, but Avraham—with the letter hei added to his name—was able to father children. In this manner, the original name had been an impediment to blessing. Alternately, a name change can indicate a type of rebirth like the process of teshuvah (repentance), and the needed blessing can then be channeled to this “new” individual. The most common situation which calls for a name-change is for a choleh (sick person) in the case of critical illness, lo aleinu. (If the choleh does not recover, chas veshalom, halachah dictates that the new name is no longer relevant, and should not be used. But if the choleh recovers, the added name remains part of their name, even if they pass away at a later time.)
There are times when people may otherwise wish to change their name. When it comes to shidduchim, for example, shinui hashem may be warranted, since many are careful that a prospective in-law not share a name with the bride or groom (see Halachah # 370). In these cases, it is the accepted practice to consult with a chacham (an especially learned person) who will weigh the current circumstances and may offer suggestions for appropriate names. We are cautious not to make these decisions except under guidance, since “messing” with our spiritual makeup in this way may be potentially damaging.
Shinui hashem (under the proper halachic guidelines) usually occurs before the Torah, when a specific mi shebeirach (prayer for an individual at the end of a Torah reading portion) is recited in front of a minyan (prayer quorum [of ten men]). (The subject of the name change—man or woman—need not be present.) The custom is not to drop the old name; the new name is added to the existing one, and becomes the first of the given names. The new name should be used for at least thirty days so it becomes a name that is muchzak (halachically established); we should be sure to call the individual with their new name (in addition to the original one) so that it does not become nishtaka (obsolete, see Halachah # 469).
* See Halachah # 514 about the writing of a kesubah when someone was subject to shinui hashem.
https://asktherav.com/25660-adding-a-name-for-a-very-ill-person/